To GUEST,one line in print

Short extracts are very common in journal articles and in books of literary criticism. They must be only a small proportion of the full work (maybe even a whole paragraph from a novel, but only a couple of lines from a shorter poem). It is called 'fair use' and is allowed if the purpose is for criticism, or for a review, or when reporting a current event.

But, as r.padgett said, a proper reference must be included, either in the text or more usually in a footnote or endnote.