Deuteronomy 21:17
He should acknowledge the firstborn son of the unloved wife. And give him a double portion of all that he has. He is the beginning of his strength. The right of the firstborn belongs to him.
Genesis 49:3
Reuben, you are my firstborn; you are my strength and the first child of my manhood. You are the proudest and strongest of all my sons.
Genesis 25:31-34
Jacob answered: I will give it to you if you give me your birthright as the firstborn son.
Genesis 25:5-6
Abraham left everything he owned to Isaac.
1 Chronicles 5:1-2
The sons of Reuben the firstborn of Israel he was the firstborn, but when he defiled his father's marriage bed, his rights as firstborn were given to the sons of Joseph son of Israel; so he could not be listed in the genealogical record in accordance with his birthright,
Psalm 105:36
He killed all the firstborn sons, the first ones born in the land when their fathers were young.