Parashas Bo · Shemos 12:1 · TT note 3
Chabad.org — English translation + Rashi
Torah Temimah on Shemos 12:1, note 3 (on לֵאמֹר) points to Mechilta / R’ Yishmael.
Sefaria — Exodus 12:1
Sefaria — Torah Temimah on Exodus 12:1
Sefaria — Mechilta
English: “Saying (leimor)” — what does leimor mean? Rabbi Yishmael said: Go out and say to them at once, as it is said, “And he went out and spoke to the children of Yisrael that which he was commanded.”
Derash on לֵאמֹר: immediate transmission of the dibbur to Yisrael.
Moshe was to convey Hashem’s words to Yisrael immediately upon receiving them.