I feel like it is pertinent to point out that, in most cases, scientific publications are meant to build on existing work. Plagiarising words and sentences verbatim, without being able to bring an original spin is simply not publication ready.

Essentially if it is a very basic tenet of your field then you will never need to mention it, you may simply cite a standard book and move ahead to present your work. There are word and page limits as well.

I believe this question arises mostly while writing reports and other "unoriginal" documents.