Parashas Bo · Shemos 12:6 · TT on לְמִשְׁמֶרֶת
Chabad.org — English translation + Rashi
Torah Temimah on Shemos 12:6 (on לְמִשְׁמֶרֶת / four days of inspection) points to Pesachim 96a.
Sefaria — Exodus 12:6
Sefaria — Torah Temimah on Exodus 12:6
Sefaria — Pesachim 96a
E-Daf — Pesachim 96a
English: “And it shall be for you a keeping until the fourteenth day of this month” — this one requires inspection four days before slaughter.
Halachic derash from לְמִשְׁמֶרֶת: the four-day gap implies required examination of the animal before slaughter.
The Pesach (and, by extension in the sugya, related offerings) must be inspected during the days of keeping before slaughter.