I submitted a paper and received reviewers' comments on it. Would using an exact sentence (just a single sentence) that one reviewer used in their comments be considered plagiarism? The sentence is so beautifully put that I can't say it any better.
The comment is:
The problem is X. Maybe you can try Y.
I did Y, and to motivate why I did Y in the text, I added a paragraph, and I want to use "The problem is X" in that paragraph. I'm afraid that I would alter the meaning by changing the wording.
Reviewers know very well that their suggestions and comments may end up in the final publication. This is the point of reviewing, and no reviewer would (or should) consider it plagiarism if sentences are copied verbatim. Having said that, it is always best to err on the side of caution, so the best course of action would be to let the editor know exactly what you did. You will contact the editor anyway with the revisions, and it is only natural to state that you used the reviewer's quote.
If you want, you can acknowledge the "anonymous reviewer" or ask the editor, and thereby indirectly the reviewer, whether they wish to be acknowledged by name (they will probably decline, but they would be happy at being offered the choice).
Personally, I once was acknowledged as "anonymous reviewer" for a model proposed based on the data in the paper (they used an entire figure I sent them). I fully expected the authors to use my image and model (why else would I have sent it?), but the acknowledgement came as a surprise and made me happy.
In many cases, the answer will be that it is perfectly natural and fine to use the same formulation as a referee. If a referee comments "In the second paragraph, you may want to point out that all Flimflams are green."; then adding "All Flimflams are green." to that paragraph is not plagiarism. The reason is that stating a fact is not plagiarism, and here the manner of stating it has no intellectual value in itself.
However, your case is different. Rather than copying a completely mundane sentence, you are tempted by a particularly beautiful sentence. There clearly is intellectual value in the formulation. Thus, you should put it in as a quote attributed to the anonymous referee.
As comments by a referee are meant to improve the article, and their name wouldnt be attached to the quote anyway, I don't see any need to ask for permission unless there is something potentially contentious about the quote.
If you use something you need to cite it. And quote it in the current situation. You may want to get permission to do so to keep it clean, but you can cite it as a comment from a reviewer in a "private communication" if nothing else is open to you.
But make sure that you don't leave the impression that the words/ideas are yours.
