Pesachim 44A

לענין חמץ בפסח נמי.

with regard to the matter of leavened bread on Passover one should also be liable for eating a prohibited substance joined together with a permitted substance.

אין הכי נמי. ולאפוקי מדאביי דאמר: יש הקטרה לפחות מכזית, קמשמע לן דהקטרה לאו לפחות מכזית.

The Talmud answers: Yes, indeed it is so, and the prohibition mentioned by Ze’eiri against sacrificing leaven in offerings was only to exclude the statement of Abaye, who said: There is significance to offering less than an olive-bulk of leaven on the altar, and one is flogged for sacrificing an offering of that kind. By noting that one is liable because permitted substances combine with prohibited substances, the baraita teaches us that an offering of less than an olive-bulk is not considered an offering, and therefore sacrificing it is not punishable by lashes.

יתיב רב דימי וקאמר לה להא שמעתא. אמר ליה אביי לרב דימי: וכל איסורין שבתורה אין היתר מצטרף לאיסור?

Rav Dimi sat and stated this halakha that a permitted substance does not join together with a prohibited substance to constitute the requisite measure, except in the case of a nazirite. Abaye said to Rav Dimi: And is it true that with regard to all other prohibitions in the Torah, a permitted substance does not join together with a prohibited substance?

והתנן: המקפה של תרומה והשום והשמן של חולין, ונגע טבול יום במקצתן ⁠— פסל את כולן. המקפה של חולין והשום והשמן של תרומה, ונגע טבול יום במקצתן ⁠— לא פסל אלא מקום מגעו בלבד.

But didn’t we learn in a Mishnah: With regard to thick soup prepared with teruma produce whose garlic and oil are of non-sacred produce, and one who immersed himself during that day touched some of the ingredients, he disqualified all the contents of the pot, as they are subsumed within the teruma soup. However, if the thick soup was prepared with non-sacred produce and the garlic and the oil were of teruma, and one who immersed himself during that day touched some of them, he disqualifies only the ingredients in the place that he touched.