And the 45th mitzvah is that we are commanded to bring an offering in addition [to the daily offerings1] also on the 50th day from the Omer offering on the 16th of Nissan. This is the musaf Atzeres2 offering.

It is mentioned in Bamidbar Sinai,3 in G‑d's statement, "On the day of the first fruits, when you bring a new grain offering4 to G‑d ... you shall bring a burnt-offering as a pleasing fragrance to G‑d [of two young bulls, one ram and seven yearling sheep]."