Exodus 4:21-25

And the Lord said to Moses, “When you go back to Egypt, see that you perform before Pharaoh all the wonders which I have put in your power; but I will harden his heart so that he will not let the people go.

Then you shall say to Pharaoh, ‘This is what the Lord says: “Israel is My son, My firstborn.

So I said to you, ‘Let My son go so that he may serve Me’; but you have refused to let him go. Behold, I am going to kill your son, your firstborn.” ’ ”

But it came about at the overnight encampment on the way, that the Lord met Moses, and sought to put him to death.

So Zipporah took a flint and cut off her son’s foreskin and threw it at Moses’ feet; and she said, “You are indeed a groom of blood to me!”