(c.f. How to ask a good question's Include source / motivation for your question and the preceeding discussion in Is it a good idea to include source from where a question is taken?)
Occasionally, I find an exercise without the source disclosed, and I know where it is from (with certainty). In the past, I would just edit this into the question: posting it as a comment is no harder, and it adds context. I have enough rep to avoid the suggested edits queue, but if I saw such a suggested edit I would vote to approve it. Often the OP is appreciative.
But a couple months back* I found an OP who reverted my edit, saying something to the effect that the question was 'too basic' or 'too simple' (I don't recall exactly) and did not need the source. So I didn't push it too hard and left the source in the comments.
Should I edit posts or leave comments in the future? Is there any good reason why an OP would not want the source in the post? The only non-negative reason I can think of is clutter, but to me that's a rather weak reason. Should I bother with a flag if my edits are reverted?
* I waited to see if an obvious answer escaped me, and also to help disassociate this meta post from it. Of course, its probably findable via SEDE (question iirc is about basic properties of $\overline \partial_z$ from one of Terry Tao's notes, if you must look)