user11482: I desperately need quotes from either scripture or from scholars.

user-1: The Sakadagami is mentioned in SN 55:24 - Sarakaani Sutta:

"Take the case of another man. He is endowed with unwavering devotion to the Buddha, the Dhamma, the Sangha. But he is not joyous in wisdom and has not gained release. Yet by destroying three fetters and weakening lust, hatred and delusion, he is a Once-returner, who will return once more to this world and put an end to suffering. That man is entirely freed from... states of woe."


user254: 
This might be the definition (it is, at least, one of the places where it's defined):

"In the Dhamma thus well-proclaimed by me — clear, open, evident, stripped of rags — those monks who have abandoned the three fetters, with the attenuation of passion, aversion, & delusion, are all once-returners who, on returning only one more time to this world, will make an ending to stress. This is how the Dhamma well-proclaimed by me is clear, open, evident, stripped of rags.

Alagaddupama Sutta: The Water-Snake Simile (MN 22)
This is summarized (and clarified) in this Wikipedia article: The four stages of attainment.
This search returns about another 50 results from the suttas: https://suttacentral.net/search?query=%22once-returner%22&lang=en


11482: <p>I desperately need quotes from either scripture or from scholars.</p>
 -1: <p>The Sakadagami is mentioned in <a href="http://www.accesstoinsight.org/tipitaka/sn/sn55/sn55.024.wlsh.html" rel="nofollow noreferrer"><em>SN 55:24 - Sarakaani Sutta</em></a>:</p>

<blockquote>
  <p><em>"Take the case of another man. He is endowed with unwavering devotion to the Buddha, the Dhamma, the Sangha. But he is not joyous in wisdom and has not gained release. Yet by destroying three fetters and weakening lust, hatred and delusion, he is a Once-returner, who will return once more to this world and put an end to suffering. That man is entirely freed from... states of woe."</em></p>
</blockquote>
 254: <ul>
<li><p>This might be the definition (it is, at least, one of the places where it's defined):</p>

<blockquote>
  <p>"In the Dhamma thus well-proclaimed by me — clear, open, evident, stripped of rags — those monks who have abandoned the three fetters, with the attenuation of passion, aversion, &amp; delusion, are all once-returners who, on returning only one more time to this world, will make an ending to stress. This is how the Dhamma well-proclaimed by me is clear, open, evident, stripped of rags.</p>
</blockquote>

<p><a href="http://www.accesstoinsight.org/lib/authors/narada/nutshell.html" rel="nofollow noreferrer">Alagaddupama Sutta: The Water-Snake Simile (MN 22)</a></p></li>
<li><p>This is summarized (and clarified) in this Wikipedia article: <a href="https://en.wikipedia.org/wiki/Four_stages_of_enlightenment#The_four_stages_of_attainment" rel="nofollow noreferrer">The four stages of attainment</a>.</p></li>
<li><p>This search returns about another 50 results from the suttas: <a href="https://suttacentral.net/search?query=%22once-returner%22&amp;lang=en" rel="nofollow noreferrer">https://suttacentral.net/search?query=%22once-returner%22&amp;lang=en</a></p></li>
</ul>
