23 and I have said to you, “Let my son go, that he may serve me;” and you have refused to let him go. Behold, I will kill your firstborn son.’”
Exodus 4:23 Cross References - WEB
Exodus 5:1
1 Afterward Moses and Aaron came, and said to Pharaoh, “This is what Yahweh, the God of Israel, says, ‘Let my people go, that they may hold a feast to me in the wilderness.’”
Exodus 7:16
16 You shall tell him, ‘Yahweh, the God of the Hebrews, has sent me to you, saying, “Let my people go, that they may serve me in the wilderness. Behold, until now you haven’t listened.”
Exodus 11:5
5 and all the firstborn in the land of Egypt shall die, from the firstborn of Pharaoh who sits on his throne, even to the firstborn of the female servant who is behind the mill, and all the firstborn of livestock.
Exodus 12:29
29 At midnight, Yahweh struck all the firstborn in the land of Egypt, from the firstborn of Pharaoh who sat on his throne to the firstborn of the captive who was in the dungeon, and all the firstborn of livestock.
Psalms 78:51
51 and struck all the firstborn in Egypt, the chief of their strength in the tents of Ham.
Psalms 105:36
36 He struck also all the firstborn in their land, the first fruits of all their manhood.
Psalms 135:8
8 He struck the firstborn of Egypt, both of man and animal.