Exodus 4:20-25

ISV(i) 20 So Moses took his wife and son, put them on donkeys, and headed back to the land of Egypt. Moses took the staff of God in his hand.
21 Then the LORD told Moses, “When you set out to return to Egypt, keep in mind all the wonders that I’ve put in your power, so that you may do them before Pharaoh. But I’ll harden his heart so that he won’t let the people go. 22 You are to say to Pharaoh, ‘This is what the LORD says: “Israel is my firstborn son. 23 And I say to you, ‘Let my son go so he may serve me. If you refuse to let him go, then I will kill your firstborn son.’”’”
24 Zipporah Circumcises Moses’ SonBut later on, at the lodging place along the way, the LORD met Moses and was about to kill him. 25 Zipporah took a flint knife, cut off her son’s foreskin, and touched Moses’ feet with it, saying while doing so, “…because you are a bridegroom of blood to me.”