Parashas Ki Sisa · Passuk 34:25
Torah Temimah points to classical source on this unit (verified).
English: “You shall not slaughter with leaven” — prohibition of slaughtering the Pesach over chametz.
Derash on not slaughtering the Pesach sacrifice over chametz, and not leaving overnight.
You shall not slaughter the blood of My sacrifice with leaven, and the sacrifice of the Festival of Pesach shall not remain overnight until morning.