Exodus 4:23

4:23 and I said to you, ‘Let my son go that he may serve me,’ but since you have refused to let him go, I will surely kill your son, your firstborn!”’”

Exodus 6:14

The Ancestry of the Deliverer

6:14 These are the heads of their fathers’ households:

The sons of Reuben, the firstborn son of Israel, were Hanoch and Pallu, Hezron and Carmi. These were the clans of Reuben.

Exodus 13:13

13:13 Every firstling of a donkey you must redeem with a lamb, and if you do not redeem it, then you must break its neck. Every firstborn of your sons you must redeem.