There is a frequently cited midrash that we read "Guard the Matzos" as "Guard the Mitzvos". I see this cited all over the internet, but no one seems to give the exact source. Could someone let me know what it is?
Relatedly, I've seen a citation to Mekhilta Shemos 12 for the statement "When a Mitzvah comes into your hand, don't let it become chametz." Is the Mekhilta the source for both statements? And does anyone know more specifically where in Ch. 12 it appears?
Thanks.