Deuteronomy 21:17

17but he shall acknowledge the firstborn, the son of the unloved, by giving him a double portion of all that he has, for he is athe firstfruits of his strength. bThe right of the firstborn is his.

1 Chronicles 5:1

Descendants of Reuben

1The sons of Reuben the firstborn of Israel ( cfor he was the firstborn, but because dhe defiled his father’s couch, ehis birthright was given to the sons of Joseph the son of Israel, so that he could not be enrolled as the oldest son;
Copyright information for ESV