Deuteronomy 16:4
And there shall be no leavened bread seen with thee in all thy coast seven days; neither shall there any thing of the flesh, which thou sacrificedst the first day at even, remain all night until the morning. And there shall be no leavened bread seen with thee in all thy coast seven days; neither shall there any thing of the flesh, which thou sacrificedst the first day at even, remain all night until the morning.
The instruction belongs to the directions given to Israel for the Passover observance. That observance was appointed to be kept annually as a yearly commemoration. The requirement concerning leavened bread through the seven days and the disposal of the flesh sacrificed on the first day at evening forms part of that yearly order.