Exodus 4:20-26

20And Moses took his wife and his sons, and set them upon a donkey, and he returned to the land of Egypt: and Moses took the rod of God in his hand. 21And the LORD said to Moses, When thou goest to return into Egypt, see that thou perform all those wonders before Pharaoh, which I have put in thy hand: but I will harden his heart, that he shall not let the people go. 22And thou shalt say to Pharaoh, Thus saith the LORD, Israel is my son, even my firstborn: 23And I say to thee, Let my son go, that he may serve me: and if thou shalt refuse to let him go, behold, I will slay thy son, even thy firstborn.

24And it came to pass by the way in the inn, that the LORD met him, and sought to kill him. 25Then Zipporah took a sharp stone, and cut off the foreskin of her son, and cast it at his feet, and said, Surely a bloody husband art thou to me.12 26So he let him go: then she said, A bloody husband thou art, because of the circumcision.