Parashas Bo · Shemos 12:10 · TT note 1
Torah Temimah on Shemos 12:10, note 1 (on עַד בֹּקֶר) points to Shabbos 24b (Tanna de-bei Chizkiyah).
Sefaria — Exodus 12:10
Sefaria — Torah Temimah on Exodus 12:10
Sefaria — Shabbos 24b
E-Daf — Shabbos 24b
English: Why does Scripture say “until morning”? The verse provides a second morning for its burning.
Textual inference from the repeated phrase “until morning.”
Leftover Pesach is not burned on the Festival itself, but on the following morning (the second “morning”).