Exodus 12:15

12:15 For seven days you must eat bread made without yeast. Surely on the first day you must put away yeast from your houses because anyone who eats bread made with yeast from the first day to the seventh day will be cut off from Israel.

Leviticus 23:7

23:7 On the first day there will be a holy assembly for you; you must not do any regular work.

Leviticus 23:10-11

23:10 “Speak to the Israelites and tell them, ‘When you enter the land that I am about to give to you and you gather in its harvest, then you must bring the sheaf of the first portion of your harvest to the priest, 23:11 and he must wave the sheaf before the Lord to be accepted for your benefit – on the day after the Sabbath the priest is to wave it.

Leviticus 23:15

The Festival of Weeks

23:15 “‘You must count for yourselves seven weeks from the day after the Sabbath, from the day you bring the wave offering sheaf; they must be complete weeks.

Deuteronomy 16:9

The Festival of Weeks

16:9 You must count seven weeks; you must begin to count them from the time you begin to harvest the standing grain.