user-1: In the Milindapanha, Nagasena points out to king Milinda that doing evil knowingly accrues lesser demerit than doing evil unknowingly. Does the Buddha make the same statement anywhere in the Suttas?

The king asked: "Venerable Nagasena, for whom is the greater demerit, one who knowingly does evil, or one who does evil unknowingly?"
The elder replied: "Indeed, your majesty, for him who does evil not knowing is the greater demerit."
"In that case, venerable Nagasena, would we doubly punish one who is our prince or king's chief minister who not knowing does evil?"
"What do you think, your majesty, who would get burned more, one who knowing picks up a hot iron ball, ablaze and glowing, or one who not knowing picks it up?"
"Indeed, venerable sir, he who not knowing picks it up would get burned more."
"Indeed, your majesty, in the same way the greater demerit is for him who does evil not knowing."
"You are clever, venerable Nagasena."

Milindapanha - Access to Insight
My interpretation of this is not about unintended action vs intended action as one of the answers suggests. Instead I see it as comparing intended action with the view that the action is unwholesome vs intended action with the view that the action is wholesome. It's not about intending harm vs not intending harm, instead it's about intending harm knowing that causing harm is bad vs intending harm not knowing that causing harm is bad.

user5715: With regard to karma one of the most cited Pāli passages is:

Cetanāhaṃ bhakkhave kammaṃ vadāmi - AN 6.63
Intention, monks, is what I call action. 

In other words, only intentional actions are karma. On the other hand Jains considered that all actions whatever were karmic. They developed the idea that inactivity was the best religious practice, taking it as far as starving themselves to death. 
This passage from Miln seems to contradict this important principle. It is very curious. I will have to give this a good deal more thought. 
And I think it's fair to say that just because someone can come up with the plausible reading of this text by changing the meaning of the words somewhat, doesn't mean that this is what was intended. A more sound procedure is to exhaust the possibilities of the text itself, then look for a traditional commentary, before starting to make ad hoc assumptions that simply fit a desired interpretation. One always has to allow that the text simply does not make sense.
~
In checking the Pāḷi passage (Miln 84) (in the Burmese 6th council Ed.) I had to translate it anyway, So I'll include my translation for reference. If there are any supplementary questions about the translation, leave a comment, and I'll edit this answer to try to explain. 

Jānantājānantapāpakaraṇapañho
The question on doing evil knowingly or unknowingly.
Rājā āha "bhante nāgasena, yo jānanto pāpakammaṃ karoti, yo ajānanto pāpakammaṃ karoti, kassa bahutaraṃ apuññan" ti?
  The King said, "Bhante Nāgasena, he who does an evil action (pāpakamma) knowingly (jānanto), he who does an evil action unknowingly (ajānanto); which has the greater demerit (apuñña)."
Thero āha "yo kho, mahārāja, ajānanto pāpakammaṃ karoti, tassa bahutaraṃ apuññan" ti.
  The Elder said, "Majesty, he who does an evil action unknowingly, he has the greater demerit" 
"Tena hi, bhante nāgasena, yo amhākaṃ rājaputto vā rājamahāmatto vā ajānanto pāpakammaṃ karoti, taṃ mayaṃ diguṇaṃ daṇḍemā" ti?
  "By this [reasoning], Bhante Nāgasena, should we punish our royal son or royal minister twofold (diguṇa) for doing an evil action unknowingly?"
"Taṃ kiṃ maññasi, mahārāja, tattaṃ ayoguḷaṃ ādittaṃ sampajjalitaṃ sajotibhūtaṃ eko jānanto gaṇheyya, eko ajānanto gaṇheyya, katamo balavataraṃ ḍayheyyā" ti.
  "What do you think, Majesty, if someone were to knowingly grasp a glowing iron ball, aflame, burning, or to unknowingly grasp it, who would receive the worse burn?" 
Yo kho, bhante, ajānanto gaṇheyya, so [tassa] balavataraṃ ḍayheyyā" ti.
  "Bhante, the one who grasped it unknowingly, he would receive the worst burn."
"Evameva kho, mahārāja, yo ajānanto pāpakammaṃ karoti, tassa bahutaraṃ apuññan" ti.
  "Just so, Majesty. he who does an evil action unknowingly, makes the most demerit." 
"Kallosi, bhante nāgasenā" ti.
  "You are skilled, Bhante Nāgasena". 

There is a lot here to digest. If Nāgasena is correct, why does Milinda say he should punish members of the royal court twofold (diguṇa)? I don't see the logic of this. 
Does the analogy even work? Is it true that grasping a burning iron ball on purpose would mean one would be burned less? Who would grasp a burning hot iron ball on purpose anyway? 
This is one of the most bizarre pieces of Pāḷi prose I've ever looked at!
I don't see how one can separate intention and understanding. Jānanto is just a very broad word for "knowing". So we must interpret yo ajānanto pāpakammaṃ karoti as "does an evil action without knowing that he does evil" and yo jānanto pāpakammaṃ karoti "does an evil action knowing that he does evil". The one who acts with knowing clearly must incur the greater consequences, but this text reverses the natural order. On face value it simply does not make sense.
It has been suggested by @RobM that this passage is referring not to the ethical quality of the action (and therefore of the vipāka it will generate), but to weightiness of the kamma. In fact I do not see any meaningful separation of these, since it is the ethical quality of an action that determines how weighty it is. Furthermore the passage itself is talking about who accrues the most apuñña or demerit. How can one separate puñña/apuñña from the "ethical quality of the action that generates it? An action generates puñña/apuñña in precise proportion to the kusala/akusala of the intention (cetanā) behind it. What's more the passage does not contain any word implying weightiness (garu, garutara, garutā etc). So although @RobM has produced a reading that is consistent with his understanding (and therefore pleasing), it is unrelated to the words he is attempting to interpret. This is an unsound exegetical methodology. 
The exegetical strategy of all those answers so far which claim to understand this passage (which I do not) is that the words jānanto/ajānanto mean something other than what they mean. Either ajānanto means micchādiṭṭhi or it means garutā (weightiness) or something else that makes the passage make simple sense. In order to establish such a reading the person proposing it would need to show that this esoteric substitution was a regular feature of either the Milindapañha or the Pāḷi literature as a whole. One of the attractions of the Pāḷi literature is that on the whole it is quite straightforward. Metaphors and similes are occasionally reified by later tradition, but they stand out in the texts. So, on the face of it, an esoteric reading, where the text says one thing but means another would require some strong evidential support in the form of many quotations of similar substitutions. I don't see any evidence to date. So far I have not understood this text, but I don't believe that anyone else has either. "Don't know" must always be a possible, if unsatisfactory solution to any problem. And if one does not know then there is no shame in saying so. To over-ride unknowing and superimpose something familiar on a text to force it into a familiar pattern is not a good practice. At best it is a form of self-deception.

user2282: Ven. Pesala's translation has a footnote to clarify the meaning:

"All wrong-doing is rooted in ignorance, so one who does wrong knowingly will feel remorse and correct himself sooner than one who is deluded (Editor’s Note)."

So based on his note, "knowingly" here means knowing that the unwholesome deed does create unwholesome results.

user5779: The source is Miln III,7,8 [84].
The other day, I happened to read a discussion of this passage in "Development in the Early Buddhist Concept of Kamma/Karma" by James Paul McDermott (page 113-114).
Based on what I have read, I do not believe that there is any specific quote in the Suttas / Vinaya that specifically supports this passage. The Suttas (AN 6.63) equate kamma with volition / intention and as McDermott explains, this was developed in the Abhidhamma (particularly the Kathāvatthu), further developed in Milindapañha and even further developed in the Abhidharmakośa. Of course, the commentaries developed the concept of kamma to a new level again (this was beyond the scope of McDermott's book).
One has to be careful with interpreting this parable of getting burned by the hot iron. The point is that a unskillful act done with wrong view will generate more weighty kamma... somebody who knows that the unskillful act is wrong will have less volition / intention when performing the unskillful act as compared to another person who sees absolutely nothing wrong with the unskillful act (i.e. accompanied by wrong view). 
@Jayarava, I have admired some of your writings / posts. Thanks for prompting me to look deeper at this passage (I love to learn). Here is the passage in Pāḷi:

Rājā āha ‘‘bhante nāgasena, yo jānanto pāpakammaṃ karoti, yo ajānanto pāpakammaṃ karoti, kassa bahutaraṃ apuñña’’nti? Thero āha ‘‘yo kho, mahārāja, ajānanto pāpakammaṃ karoti, tassa bahutaraṃ apuñña’’nti. ‘‘Tena hi, bhante nāgasena, yo amhākaṃ rājaputto vā rājamahāmatto vā ajānanto pāpakammaṃ karoti, taṃ mayaṃ diguṇaṃ daṇḍemā’’ti? ‘‘Taṃ kiṃ maññasi, mahārāja, tattaṃ ayoguḷaṃ ādittaṃ sampajjalitaṃ sajotibhūtaṃ eko jānanto gaṇheyya, eko ajānanto gaṇheyya, katamo [kassa (ka.)] balavataraṃ ḍayheyyā’’ti. ‘‘Yo kho, bhante, ajānanto gaṇheyya, so [tassa (pī. ka.)] balavataraṃ ḍayheyyā’’ti. ‘‘Evameva kho, mahārāja, yo ajānanto pāpakammaṃ karoti, tassa bahutaraṃ apuñña’’nti.

I believe that the key word is "ajānanto". In the translation above, it is rendered as "unknowingly". T.W. Rhys Davids translates this as "inadvertently". Bhikkhu Pesala translates this as "unconsciously". PED uses translations such as "unaware" and "unsuspecting".
I do not think "ajānanto" is equivalent to "ignorance" (delusion / moha). "Ajānanto" seems to be closer to "unwise attention", not seeing things as they truly are. For this reason, I think wrong view is a better handling, even though "micchādiṭṭhi" is not used in the text. @Jayarava, your knowledge of Pāḷi is far superior to mine, so I would be very willing to be corrected. 
Oops, I just read your answer below, so let me add more...
I am an Abhidhamma teacher and this certainly colours my world view :-) Let me put an Abhidhamma spin on this to see if it helps. The Milindapañha was written after the Abhidhamma, so it is possible that in this passage, Nāgasena is attempting to clarify a doubt from the Abhidhamma.
Kamma comes from intention. The ethical quality of the kamma created comes from the roots (attachment / aversion / delusion for unwholesome, non-attachment / non-aversion / understanding for wholesome). 
I do not believe that this passage from the Milindapañha is talking about the ethical quality of the kamma created. 
I do believe that this passage from the Milindapañha is talking about the weightiness / intensity of the kamma created... and this is a different issue. The weightiness / intensity of the kamma created is a question of strength of volition.
In the case of unwholesome kamma-creating mental states, the strength of volition can depend on pleasant / neutral feeling (pleasant feeling contributes to stronger volition), prompted / spontaneous (spontaneous contributes to stronger volition) and associated / disassociated with wrong view (associated with wrong view contributes to stronger volition). I believe that this passage from the Milindapañha is talking about the third factor; "associated / disassociated with wrong view".

-1: <p>In the Milindapanha, Nagasena points out to king Milinda that doing evil knowingly accrues lesser demerit than doing evil unknowingly. Does the Buddha make the same statement anywhere in the Suttas?</p>
<blockquote>
<p>The king asked: &quot;Venerable Nagasena, for whom is the greater demerit, one who knowingly does evil, or one who does evil unknowingly?&quot;</p>
<p>The elder replied: &quot;Indeed, your majesty, for him who does evil not knowing is the greater demerit.&quot;</p>
<p>&quot;In that case, venerable Nagasena, would we doubly punish one who is our prince or king's chief minister who not knowing does evil?&quot;</p>
<p>&quot;What do you think, your majesty, who would get burned more, one who knowing picks up a hot iron ball, ablaze and glowing, or one who not knowing picks it up?&quot;</p>
<p>&quot;Indeed, venerable sir, he who not knowing picks it up would get burned more.&quot;</p>
<p>&quot;Indeed, your majesty, in the same way the greater demerit is for him who does evil not knowing.&quot;</p>
<p>&quot;You are clever, venerable Nagasena.&quot;</p>
</blockquote>
<p><a href="http://www.accesstoinsight.org/tipitaka/kn/miln/miln.3x.kell.html#miln-3-7-08" rel="nofollow noreferrer">Milindapanha - Access to Insight</a></p>
<p>My interpretation of this is not about unintended action vs intended action as one of the answers suggests. Instead I see it as comparing intended action with the view that the action is unwholesome vs intended action with the view that the action is wholesome. It's not about intending harm vs not intending harm, instead it's about intending harm knowing that causing harm is bad vs intending harm not knowing that causing harm is bad.</p>
 5715: <p>With regard to karma one of the most cited Pāli passages is:</p>

<blockquote>
  <p><em>Cetanāhaṃ bhakkhave kammaṃ vadāmi</em> - AN 6.63</p>
  
  <p>Intention, monks, is what I call action. </p>
</blockquote>

<p>In other words, only intentional actions are karma. On the other hand Jains considered that all actions whatever were karmic. They developed the idea that inactivity was the best religious practice, taking it as far as starving themselves to death. </p>

<p>This passage from Miln seems to contradict this important principle. It is very curious. I will have to give this a good deal more thought. </p>

<p>And I think it's fair to say that just because someone can come up with the plausible reading of this text by changing the meaning of the words somewhat, doesn't mean that this is what was intended. A more sound procedure is to exhaust the possibilities of the text itself, then look for a traditional commentary, before starting to make <em>ad hoc</em> assumptions that simply fit a desired interpretation. One always has to allow that the text simply does not make sense.</p>

<p>~</p>

<p>In checking the Pāḷi passage (Miln 84) (in the Burmese 6th council Ed.) I had to translate it anyway, So I'll include my translation for reference. If there are any supplementary questions about the translation, leave a comment, and I'll edit this answer to try to explain. </p>

<blockquote>
  <p><strong><em>Jānantājānantapāpakaraṇapañho</em></strong><br>
  <strong>The question on doing evil knowingly or unknowingly.</strong></p>
  
  <p><em>Rājā āha "bhante nāgasena, yo jānanto pāpakammaṃ karoti, yo ajānanto pāpakammaṃ karoti, kassa bahutaraṃ apuññan" ti?</em><br>
  The King said, "Bhante Nāgasena, he who does an evil action (<em>pāpakamma</em>) knowingly (<em>jānanto</em>), he who does an evil action unknowingly (<em>ajānanto</em>); which has the greater demerit (<em>apuñña</em>)."</p>
  
  <p><em>Thero āha "yo kho, mahārāja, ajānanto pāpakammaṃ karoti, tassa bahutaraṃ apuññan" ti.</em><br>
  The Elder said, "Majesty, he who does an evil action unknowingly, he has the greater demerit" </p>
  
  <p><em>"Tena hi, bhante nāgasena, yo amhākaṃ rājaputto vā rājamahāmatto vā ajānanto pāpakammaṃ karoti, taṃ mayaṃ diguṇaṃ daṇḍemā" ti?</em><br>
  "By this [reasoning], Bhante Nāgasena, should we punish our royal son or royal minister twofold (diguṇa) for doing an evil action unknowingly?"</p>
  
  <p><em>"Taṃ kiṃ maññasi, mahārāja, tattaṃ ayoguḷaṃ ādittaṃ sampajjalitaṃ sajotibhūtaṃ eko jānanto gaṇheyya, eko ajānanto gaṇheyya, katamo balavataraṃ ḍayheyyā" ti.</em><br>
  "What do you think, Majesty, if someone were to knowingly grasp a glowing iron ball, aflame, burning, or to unknowingly grasp it, who would receive the worse burn?" </p>
  
  <p><em>Yo kho, bhante, ajānanto gaṇheyya, so [tassa] balavataraṃ ḍayheyyā" ti.</em><br>
  "Bhante, the one who grasped it unknowingly, he would receive the worst burn."</p>
  
  <p><em>"Evameva kho, mahārāja, yo ajānanto pāpakammaṃ karoti, tassa bahutaraṃ apuññan" ti.</em><br>
  "Just so, Majesty. he who does an evil action unknowingly, makes the most demerit." </p>
  
  <p><em>"Kallosi, bhante nāgasenā" ti.</em><br>
  "You are skilled, Bhante Nāgasena". </p>
</blockquote>

<p>There is a lot here to digest. If Nāgasena is correct, why does Milinda say he should punish members of the royal court twofold (diguṇa)? I don't see the logic of this. </p>

<p>Does the analogy even work? Is it true that grasping a burning iron ball on purpose would mean one would be burned less? Who would grasp a burning hot iron ball on purpose anyway? </p>

<p>This is one of the most bizarre pieces of Pāḷi prose I've ever looked at!</p>

<p>I don't see how one can separate intention and understanding. <em>Jānanto</em> is just a very broad word for "knowing". So we must interpret <em>yo ajānanto pāpakammaṃ karoti</em> as "does an evil action without knowing that he does evil" and <em>yo jānanto pāpakammaṃ karoti</em> "does an evil action knowing that he does evil". The one who acts with knowing clearly must incur the greater consequences, but this text reverses the natural order. On face value it simply does not make sense.</p>

<p>It has been suggested by @RobM that this passage is referring not to the ethical quality of the action (and therefore of the <em>vipāka</em> it will generate), but to weightiness of the <em>kamma</em>. In fact I do not see any meaningful separation of these, since it is the ethical quality of an action that determines how weighty it is. Furthermore the passage itself is talking about who accrues the most <em>apuñña</em> or demerit. How can one separate <em>puñña/apuñña</em> from the "ethical quality of the action that generates it? An action generates <em>puñña/apuñña</em> in precise proportion to the <em>kusala/akusala</em> of the intention (<em>cetanā</em>) behind it. What's more the passage does not contain any word implying weightiness (<em>garu, garutara</em>, <em>garutā</em> etc). So although @RobM has produced a reading that is consistent with his understanding (and therefore pleasing), it is unrelated to the words he is attempting to interpret. This is an unsound exegetical methodology. </p>

<p>The exegetical strategy of all those answers so far which claim to understand this passage (which I do not) is that the words <em>jānanto/ajānanto</em> mean something other than what they mean. Either <em>ajānanto</em> means <em>micchādiṭṭhi</em> or it means <em>garutā</em> (weightiness) or something else that makes the passage make simple sense. In order to establish such a reading the person proposing it would need to show that this esoteric substitution was a regular feature of either the <em>Milindapañha</em> or the Pāḷi literature as a whole. One of the attractions of the Pāḷi literature is that on the whole it is quite straightforward. Metaphors and similes are occasionally reified by later tradition, but they stand out in the texts. So, on the face of it, an esoteric reading, where the text <em>says</em> one thing but <em>means</em> another would require some strong evidential support in the form of many quotations of similar substitutions. I don't see any evidence to date. So far I have not understood this text, but I don't believe that anyone else has either. "Don't know" must always be a possible, if unsatisfactory solution to any problem. And if one does not know then there is no shame in saying so. To over-ride unknowing and superimpose something familiar on a text to force it into a familiar pattern is not a good practice. At best it is a form of self-deception.</p>
 2282: <p>Ven. Pesala's <a href="http://www.buddhanet.net/pdf_file/milinda.pdf" rel="nofollow">translation</a> has a footnote to clarify the meaning:</p>

<blockquote>
  <p>"All wrong-doing is rooted in ignorance, so one who does wrong knowingly will feel remorse and correct himself sooner than one who is deluded (Editor’s Note)."</p>
</blockquote>

<p>So based on his note, "knowingly" here means knowing that the unwholesome deed does create unwholesome results.</p>
 5779: <p>The source is Miln III,7,8 [84].</p>

<p>The other day, I happened to read a discussion of this passage in "Development in the Early Buddhist Concept of Kamma/Karma" by James Paul McDermott (page 113-114).</p>

<p>Based on what I have read, I do not believe that there is any specific quote in the Suttas / Vinaya that specifically supports this passage. The Suttas (AN 6.63) equate kamma with volition / intention and as McDermott explains, this was developed in the Abhidhamma (particularly the Kathāvatthu), further developed in Milindapañha and even further developed in the Abhidharmakośa. Of course, the commentaries developed the concept of kamma to a new level again (this was beyond the scope of McDermott's book).</p>

<p>One has to be careful with interpreting this parable of getting burned by the hot iron. The point is that a unskillful act done with wrong view will generate more weighty kamma... somebody who knows that the unskillful act is wrong will have less volition / intention when performing the unskillful act as compared to another person who sees absolutely nothing wrong with the unskillful act (i.e. accompanied by wrong view). </p>

<p>@Jayarava, I have admired some of your writings / posts. Thanks for prompting me to look deeper at this passage (I love to learn). Here is the passage in Pāḷi:</p>

<blockquote>
  <p>Rājā āha ‘‘bhante nāgasena, yo jānanto pāpakammaṃ karoti, yo ajānanto pāpakammaṃ karoti, kassa bahutaraṃ apuñña’’nti? Thero āha ‘‘yo kho, mahārāja, ajānanto pāpakammaṃ karoti, tassa bahutaraṃ apuñña’’nti. ‘‘Tena hi, bhante nāgasena, yo amhākaṃ rājaputto vā rājamahāmatto vā ajānanto pāpakammaṃ karoti, taṃ mayaṃ diguṇaṃ daṇḍemā’’ti? ‘‘Taṃ kiṃ maññasi, mahārāja, tattaṃ ayoguḷaṃ ādittaṃ sampajjalitaṃ sajotibhūtaṃ eko jānanto gaṇheyya, eko ajānanto gaṇheyya, katamo [kassa (ka.)] balavataraṃ ḍayheyyā’’ti. ‘‘Yo kho, bhante, ajānanto gaṇheyya, so [tassa (pī. ka.)] balavataraṃ ḍayheyyā’’ti. ‘‘Evameva kho, mahārāja, yo ajānanto pāpakammaṃ karoti, tassa bahutaraṃ apuñña’’nti.</p>
</blockquote>

<p>I believe that the key word is "<em>ajānanto</em>". In the translation above, it is rendered as "unknowingly". T.W. Rhys Davids translates this as "inadvertently". Bhikkhu Pesala translates this as "unconsciously". PED uses translations such as "unaware" and "unsuspecting".</p>

<p>I do not think "<em>ajānanto</em>" is equivalent to "ignorance" (delusion / <em>moha</em>). "<em>Ajānanto</em>" seems to be closer to "unwise attention", not seeing things as they truly are. For this reason, I think wrong view is a better handling, even though "<em>micchādiṭṭhi</em>" is not used in the text. @Jayarava, your knowledge of Pāḷi is far superior to mine, so I would be very willing to be corrected. </p>

<p>Oops, I just read your answer below, so let me add more...</p>

<p>I am an Abhidhamma teacher and this certainly colours my world view :-) Let me put an Abhidhamma spin on this to see if it helps. The Milindapañha was written after the Abhidhamma, so it is possible that in this passage, Nāgasena is attempting to clarify a doubt from the Abhidhamma.</p>

<p>Kamma comes from intention. The ethical quality of the kamma created comes from the roots (attachment / aversion / delusion for unwholesome, non-attachment / non-aversion / understanding for wholesome). </p>

<p>I <strong>do not</strong> believe that this passage from the Milindapañha is talking about the ethical quality of the kamma created. </p>

<p>I <strong>do</strong> believe that this passage from the Milindapañha is talking about the weightiness / intensity of the kamma created... and this is a different issue. The weightiness / intensity of the kamma created is a question of strength of volition.</p>

<p>In the case of unwholesome kamma-creating mental states, the strength of volition can depend on pleasant / neutral feeling (pleasant feeling contributes to stronger volition), prompted / spontaneous (spontaneous contributes to stronger volition) and associated / disassociated with wrong view (associated with wrong view contributes to stronger volition). I believe that this passage from the Milindapañha is talking about the third factor; "associated / disassociated with wrong view".</p>
