I am not sure if abstract can be a dependable reference. But people do refer to abstracts as major publication sites have cite buttons for their abstracts even if the full article is paywalled. If they have a reference file in bib or other formatssimply down the file and let your reference manager do the rest. Otherwise, refer to your style guide for more info. Hope this answers your concern.
I agree with Faiz Kattakath that an abstract alone is sometimes not a dependable reference. As a result, obviously, I would not cite it as such. I have found that the findings and discussion sections often contain far more useful information for me to think about and/or cite.
I agree with Faiz and Joseph! It might even be that what interests you is not located in the abstract, or that your goal is to provide some interpretation on one point or another of an article, in which case you must have access to the whole content.