Leviticus 23:14-15

¹⁴You shall not eat either bread, or parched corn, or frumenty of the harvest, until the day that you shall offer thereof to your God. It is a precept for ever throughout your generations, and all your dwellings.

¹⁵You shall count therefore from the morrow after the sabbath, wherein you offered the sheaf of the firstfruits, seven full weeks.