Q. When you repeat divrei Torah, and these should be said in the name of the author who said them, but you can’t remember who it was, should you not say them at all, or maybe say you can’t remember?

A. There are a number of mitzvos and prohibitions involved in mentioning or omitting the name of the author when repeating his words (see next answer). However many Poiskim maintain that if we declare that the ideas articulated are not our own but from our teachers or are already written in seforim and are widely known, these prohibitions do not apply. That seems to be the opinion of the Rambam in his introduction to Shmono Perokim, Ramban in his introduction to Dino Degarmi and the Remoh in the introduction to Shulchan Aruch, and others. However, not all agree, see Dovor Beshem Omro (3:9).

Horav Shlomo Miller’s Shlit”a opinion is that when you cannot remember or are in doubt as to the name of the author, it suffices to mention that fact.

Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit”a