TT #215 · Parashas Reeh · Fourth Aliyah · Passuk 14:21
You shall not eat any carcass; give it to the stranger within your gates, that he may eat it, or sell it to a foreigner; for you are a holy people to Hashem your God. You shall not boil a kid in its mother’s milk.
Torah Temimah points to Torah Temimah / Chullin.
Sefaria — Torah Temimah on Deuteronomy 14:21
English: From “or sell it to a foreigner… you shall not boil a kid” — from where is meat-in-milk forbidden in benefit? The Torah says: when you sell it, do not boil it [first].
Derash linking sale and basar be-chalav (TT) — benefit is also forbidden.
Meat cooked in milk is forbidden not only in eating but in benefit.