Exodus 13:7-10

13:7 Bread made without yeast must be eaten for seven days; no bread made with yeast shall be seen among you, and you must have no yeast among you within any of your borders.

13:8 You are to tell your son on that day, ‘It is because of what the Lord did for me when I came out of Egypt.’ 13:9 It will be a sign for you on your hand and a memorial on your forehead, so that the law of the Lord may be in your mouth, for with a mighty hand the Lord brought you out of Egypt. 13:10 So you must keep this ordinance at its appointed time from year to year.