Parashas Bo · Passuk 12:20
Chabad.org — English translation + Rashi
Torah Temimah points to Pesachim 36b (verified).
Sefaria — Exodus 12:20English: One might think that first fruits could be used for the mitzvah of matzah. “In all your settlements you shall eat matzah” excludes first fruits, which are not eaten everywhere but only in Jerusalem. The doubled “matzah” permits second tithe, which has circumstances in which it may be eaten throughout the settlements.
On the daf / in context: See the cited source for the full section.
Derash defining which consecrated produce can qualify as matzah under “in all your settlements.”
First fruits are excluded because they lack permission for consumption throughout the settlements; second tithe is included because it can have such permission.