Exodus 18:5-6

Then Jethro, his father-in-law, came with Moses’ sons and his wife to [join] Moses in the wilderness where he was camped, at the mountain of God [that is, Mt. Sinai in Horeb]. He sent a message to Moses, “I, your father-in-law Jethro, am coming to you with your wife and her two sons [who are] with her.”