Hello kolllel!

I was discussing with a friend, and had a question. Even though the rambam doesn't give sources, the choice of language will often hint to his source. In hilchot deot 4:10, the rambam ends with the language of "yifrosh meyad" in the context of normal relations. I am familiar with this phrasing in the situation where a woman becomes a niddah, and a similar idea in nedarim 20b with eim shalom, but not in the context of regular marital relations.

Are you aware of what the source for this concept in normal relations , and where in the gemara this specific wording in this context might be?

Thank you and Shabbat shalom!

Josh