Exodus 13:6-8
6 For seven days eat bread made without yeast and on the seventh day hold a festival to the Lord.
7 Eat unleavened bread during those seven days; nothing with yeast in it is to be seen among you, nor shall any yeast be seen anywhere within your borders.
8 On that day tell your son, ‘I do this because of what the Lord did for me when I came out of Egypt.’