Leviticus 23:3-6 New International Version (NIV)

3. “ ‘There are six days when you may work, but the seventh day is a day of sabbath rest, a day of sacred assembly. You are not to do any work; wherever you live, it is a sabbath to the Lord.

4. “ ‘These are the Lord’s appointed festivals, the sacred assemblies you are to proclaim at their appointed times:

5. The Lord’s Passover begins at twilight on the fourteenth day of the first month.

6. On the fifteenth day of that month the Lord’s Festival of Unleavened Bread begins; for seven days you must eat bread made without yeast.

Leviticus 23