Leviticus 23:8

But ye shall offer an offering made by, fire unto the Lord
seven days
A burnt offering was to be offered unto the Lord on everyone of the seven days, which were two young bullocks, one ram, and seven lambs; besides a meat offering, and a goat for a sin offering, ( Numbers 28:19-24 ) ; in the seventh day [is] an holy convocation, ye shall do no servile
work [therein];
as on the first day, that was on account of the Israelites going out of Egypt; and this is said, on account of Pharaoh and his host being drowned on it; (See Gill on Exodus 12:16).