Exodus 12:19

12:19 For seven days yeast must not be found in your houses, for whoever eats what is made with yeast – that person will be cut off from the community of Israel, whether a foreigner or one born in the land.

Exodus 13:7

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.