Exodus 4:20-25

20So Moses took his wife and his sons and had them ride on a donkey, and went back to the land of Egypt. And Moses took the staff of God in his hand. 21And the LORD said to Moses, “When you go back to Egypt, see that you do before Pharaoh all the miracles that I have put in your power. But I will harden his heart, so that he will not let the people go. 22Then you shall say to Pharaoh, ‘Thus says the LORD, Israel is my firstborn son, 23and I say to you, “Let my son go that he may serve me.” If you refuse to let him go, behold, I will kill your firstborn son.’” 24At a lodging place on the way the LORD met him and sought to put him to death. 25Then Zipporah took a flint and cut off her son’s foreskin and touched Moses’ feet with it and said, “Surely you are a bridegroom of blood to me!”