Is it unethical to cite a paper or book that you have never looked at? Suppose I see that Book X is cited by several papers with reference to some particular Fact Y. I wish to cite Fact Y. As far as I know, Book X is the only reference for Fact Y. 

I have never looked at Book X. Nonetheless, I cite it like this:

'Fact Y' (see Book X)

My question is: Is this ethical, given that I've never looked at Book X?

More context for my question. I am NOT asking whether this is good scientific practice. I am NOT asking how a good scientist should actually go about citing Fact Y. I am NOT asking if this could undermine your credibility as a scientist.

Instead, I am asking this question because it seems to be a somewhat-common practice. And moreover, as far as I know, no scientist has ever been issued even an official rebuke (much less fired) for engaging in such practice. This would suggest to me that this practice is not considered to be unethical. 

Of course, it is not binary as to whether a practice is unethical. But I would simply like to know whether the academic community in general considers this to be even a mildly unethical practice. Or if it is perhaps very slightly unethical, but not a big deal. Or if it is not in the least bit unethical.
When you cite a source, you are not actually claiming that you have read it.  What you are actually doing is staking your professional reputation on that source containing the information that you claim that it contains.

In most circumstances, of course, this gets instantiated exactly how you would expect: at least one of the authors has personally read the source.  There are, however, certain circumstances in which citation of an unread source is actually appropriate.  Let me give two examples:


The source is cited as a secondary source, e.g., "Feng et al.[17] claim that the species presented in the Necronomicon[18] can be found in Antarctica."  Here is is appropriate to give the bibliographic "pointer" to the secondary source even if you cannot access it yourself.
The source material may be known by a different route than the original publication.  This frequently happens with software tools and standards: for example, you might cite a standard that you are using even if you haven't read the standards document.  Likewise, if I am using a software tool, the authors often point to a particular paper as the preferred appropriate citation for the tool, and I am happy to take their word for it without reading that paper.


There may be many more cases as well.  It all comes down to this: how certain are you that you really know that the document you cite serves the purpose for which you are citing it?