Talmud - Nedarim 52a נדרים נ״ב א׳

is permitted to eat gravy and sediments of boiled meat [kifa]. But Rabbi Yehuda maintains that he is prohibited from eating them.

Rabbi Yehuda said: There was an incident where one took such a vow and Rabbi Tarfon prohibited us from even eggs that were cooked with meat. The Rabbis said to him: Indeed so, but when is this the halakha? When he says: This meat is forbidden to me, referring to a specific piece of meat. This is because in the case of one who vows that an item is forbidden to him, and it becomes mixed into another item, if the latter contains an amount of the forbidden food that gives it flavor, i.e., the forbidden food can be tasted in the permitted food, the mixture is forbidden. However, if one vows that meat in general is forbidden to him, without specifying a particular piece, only the meat itself is forbidden, not the gravy, sediments, or eggs cooked with that meat.

Likewise, one who vows that wine is forbidden to him is permitted to eat a cooked dish that has the flavor of wine. However, if he said: This wine is konam for me, and for that reason I will not taste it, and the wine fell into a cooked dish, if the dish contains an amount of the wine that gives it flavor, it is forbidden.

Traduction : The William Davidson digital edition of the Koren Noé Talmud, with commentary by Rabbi Adin Even-Israel Steinsaltz.

Nedarim 52a examines whether a vow against meat also bans gravy or eggs cooked with it, distinguishing general vows from those naming a specific piece.