Parashas Bo · Shemos 12:4 · TT note 6
Torah Temimah on Shemos 12:4, note 6 (on בְּמִכְסַת נְפָשֹׁת) points to Pesachim 89a.
Sefaria — Exodus 12:4
Sefaria — Torah Temimah on Exodus 12:4
Sefaria — Pesachim 89a
E-Daf — Pesachim 89a
English: But as for enrollment — everyone agrees [it continues] until it is slaughtered, for the verse says “according to the number of persons,” and then “you shall make your count.”
Order of the verse: first enrollment (בְּמִכְסַת), then slaughter (תָּכֹסּוּ).
Enrollment on the Pesach is valid up to the moment of slaughter, because the verse places the count before the act of slaughtering.