Leviticus 23:4-8

These are the feasts of the LORD, even holy convocations, which ye shall proclaim in their seasons. In the fourteenth day of the first month at even is the LORD's passover. And on the fifteenth day of the same month is the feast of unleavened bread unto the LORD: seven days ye must eat unleavened bread. In the first day ye shall have an holy convocation: ye shall do no servile work therein. But ye shall offer an offering made by fire unto the LORD seven days: in the seventh day is an holy convocation: ye shall do no servile work therein.