Avodah Zarah 73A

איכא דאמרי: רבה בר רב הונא גופיה אישתי בקנישקנין.

There are those who say that Rabba bar Rav Huna himself drank from a kenishkanin.

מתני׳ יין נסך אסור ואוסר בכל שהוא, יין ביין ומים במים בכל שהוא, יין במים ומים ביין בנותן טעם.

Mishnah: Wine used for a libation is forbidden, and any amount of it renders other wine forbidden if they are mixed together. Wine used for a libation that became mixed with wine, or water that was used for an idolatrous libation that became mixed with ordinary water, renders the mixture forbidden with any amount of the forbidden wine or water; but wine used for a libation that became mixed with water, or water used for a libation that became mixed with wine renders the mixture forbidden only if the forbidden liquid is sufficient to impart flavor to the mixture, i.e., for the wine to flavor the water or for the water to dilute the wine to an extent that can be tasted.

זה הכלל: מין במינו ⁠— במשהו, ושלא במינו ⁠— בנותן טעם.

This is the principle: A substance in contact with the same type of substance renders the mixture forbidden with any amount of the forbidden substance, but a substance in contact with a different type of substance renders the mixture forbidden only in a case where it imparts flavor to it.

גמ׳ כי אתא רב דימי אמר רבי יוחנן: המערה יין נסך מחבית לבור, אפילו כל היום כולו ⁠— ראשון ראשון בטל.

Talmud: When Rav Dimi came from Eretz Yisrael to Babylonia, he reported that R' Yoḥanan says: In the case of one who pours wine used for a libation from a jug into a wine cistern, even if he does this all day long, the forbidden wine is nullified little by little upon contact with the wine in the cistern, and the wine is consequently permitted.