Deuteronomy 16:5-9

MLV(i) 5 You may not sacrifice the Passover within any of your gates, which Jehovah your God gives you, 6 but at the place which Jehovah your God will choose to cause his name to dwell in, there you will sacrifice the Passover at evening, at the going down of the sun, at the season that you came forth out of Egypt. 7 And you will roast and eat it in the place which Jehovah your God will choose and you will turn in the morning and go to your tents. 8 Six days you will eat unleavened bread and on the seventh day will be a solemn assembly to Jehovah your God. You will do no work.
9 You will number to you seven weeks. From the time you begin to put the sickle to the standing grain you will begin to number seven weeks.