Exodus 13:8-10

8On that day tell your son, ‘I do this because of what the LORD did for me when I came out of Egypt.’ 9This observance will be for you like a sign on your hand and a reminder on your forehead that this law of the LORD is to be on your lips. For the LORD brought you out of Egypt with his mighty hand.

10You must keep this ordinance at the appointed time year after year.