Genesis 29:26

29:26 “It is not our custom here,” Laban replied, “to give the younger daughter in marriage before the firstborn.

Genesis 35:23

35:23 The sons of Leah were Reuben, Jacob’s firstborn, as well as Simeon, Levi, Judah, Issachar, and Zebulun.

Genesis 38:7

38:7 But Er, Judah’s firstborn, was evil in the Lord’s sight, so the Lord killed him.

Genesis 49:3

49:3 Reuben, you are my firstborn,

my might and the beginning of my strength,

outstanding in dignity, outstanding in power.