Parashas Bo · Passuk 12:20
Chabad.org — English translation + Rashi
Torah Temimah points to Pesachim 43a (verified).
Sefaria — Exodus 12:20English: “All leavened matter you shall not eat” includes mixtures such as Babylonian kutach, Median beer, Edomite vinegar, and Egyptian zitom. A mixture is subject to the prohibition, but the karet penalty applies to actual grain-hametz.
On the daf / in context: See the cited source for the full section.
Derash extending the prohibition of chametz to specified mixtures while distinguishing them from fully-fledged grain chametz.
Chametz mixtures are prohibited, but the Torah’s karet penalty is distinguished from the prohibition applying to the mixture.