Exodus 13:10
Thou shalt therefore keep this ordinance in his season from year to year.
More from Exodus 13
And the LORD spake unto Moses, saying,
Sanctify unto me all the firstborn, whatsoever openeth the womb among the children of Israel, both of man and of beast:
And Moses said unto the people, Remember this day, in which ye came out from Egypt, out of the house of bondage; for by strength of hand the LORD brought you out from this place: there shall no leavened bread be eaten.
This day came ye out in the month Abib.
And it shall be when the LORD shall bring thee into the land of the Canaanites, and the Hittites, and the Amorites, and the Hivites, and the Jebusites, which he sware unto thy fathers to give thee, a land flowing with milk and honey, that thou shalt keep this service in this month.