Exodus 4:22-26

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!”

So He left him alone. At that time she said, “You are a groom of blood”—because of the circumcision.