Deuteronomy 16:4

16:4 There must not be a scrap of yeast within your land for seven days, nor can any of the meat you sacrifice on the evening of the first day remain until the next morning.

Deuteronomy 16:8

16:8 You must eat bread made without yeast for six days. The seventh day you are to hold an assembly for the Lord your God; you must not do any work on that day.