Deuteronomy 4:20

4:20 You, however, the Lord has selected and brought from Egypt, that iron-smelting furnace, to be his special people as you are today.

Jeremiah 11:4

11:4 Those are the terms that I charged your ancestors to keep when I brought them out of Egypt, that place which was like an iron-smelting furnace. I said at that time, “Obey me and carry out the terms of the agreement exactly as I commanded you. If you do, you will be my people and I will be your God.