Leviticus 23:14-15

¹⁴Ye shall not eat a loaf, neither cake, nor pottage of the corn, till to the day in which ye shall offer thereof to your God; it is a behest everlasting in your generations, and in all your dwelling places.

¹⁵Therefore ye shall number from the tother day of the sabbath, in which ye offered handfuls of the first fruits, seven full weeks,