The Feast of the Passover: Leaven: Not to be in Any of Their Quarters
Source: TTT
Exodus 13:7
Unleavened bread shall be eaten during those seven days. Nothing leavened may be found among you, nor shall leaven be found anywhere within your borders.
Deuteronomy 16:4
No leaven is to be found in all your land for seven days, and none of the meat you sacrifice in the evening of the first day shall remain until morning.