Deuteronomy 21:17

21:17 Rather, he must acknowledge the son of the less loved wife as firstborn and give him the double portion of all he has, for that son is the beginning of his father’s procreative power – to him should go the right of the firstborn.

Deuteronomy 26:2

26:2 you must take the first of all the ground’s produce you harvest from the land the Lord your God is giving you, place it in a basket, and go to the place where he chooses to locate his name.

Deuteronomy 26:10

26:10 So now, look! I have brought the first of the ground’s produce that you, Lord, have given me.” Then you must set it down before the Lord your God and worship before him.