Deuteronomy 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.
Genesis 49:3
Reuben, you are my firstborn, my might and the beginning of my strength, outstanding in dignity, outstanding in power.
Genesis 25:31-34
But Jacob replied, "First sell me your birthright."
Genesis 25:5-6
Everything he owned Abraham left to his son Isaac.
1 Chronicles 5:1-2
The sons of Reuben, Israel's firstborn -- (Now he was the firstborn, but when he defiled his father's bed, his rights as firstborn were given to the sons of Joseph, Israel's son. So Reuben is not listed as firstborn in the genealogical records.
Psalm 105:36
He struck down all the firstborn in their land, the firstfruits of their reproductive power.