e.g., Babylonian Talmud Berakhot 62a:
Rav Kahana went in and lay down under Rav [i.e., Rabbi Abba] 's bed.
He heard him chatting and joking [with his wife] and doing what he required.
[Rav Kahana] said to him: It sounds as if Abba's mouth has never sipped a dish before!
He said to him: Kahana, are you here?! Get out, because this is not proper behaviour.
He replied: It is Torah, and I need to learn.