민수기 28:17 미드라쉬: Mekhilta DeRabbi Yishmael & Sifrei Bamidbar

R. Nathan says "Observe the month of Aviv" — Observe the month which is closest to Aviv. And which is that? Adar. But we have not heard how many (days) are to be intercalated. From "Observe the month (of Aviv"), we infer that a month (of days, i.e., thirty) are to be intercalated. And this follows, viz.: A month is intercalated and a year is intercalated. Just as a month, (with) one of its units (i.e., days), so, a year, with one of its units (i.e., months). But perhaps, just as (with a) month — one thirtieth of it, so, (with) a year, one thirtieth of it? It is, therefore, written "Observe the month." (A month is intercalated and not one thirtieth of it. But perhaps, just as a year, one twelfth of it, so, a month, one twelfth of it? It is, therefore, written (Numbers 28:17) "And on the fifteenth day of this month" — You intercalate a day for a month, and not one twelfth of it.

(Bamidbar 28:16) "And in the first month, on the fourteenth day of the month, it is Pesach to the L-rd": Scripture (here) makes it mandatory (and not optional.) (Ibid. 28:17) "for seven days matzoth shall be eaten": I might think that any matzoth (may be eaten [e.g., even those made of rice]). It is, therefore, written (Devarim 16:3) "You shall not eat chametz with it. Seven days shall you eat matzoth with it." Only that which can be matzah (unleavened) or chametz (leavened) (is forbidden in the leavened state). These are the five varieties: wheat, barley, spelt, rye, or oats. This excludes rice, millet, sesame, paragim, which never become matzah or chametz, but only decay.