Origen, on Gen 24:1

“Now Abraham was old; and advanced in age: and the Lord had blessed him in all things.”

“But indeed, we should not fail to notice from these things that are reported by the literal meaning, what generations and of what sort they are, which are propagated from Keturah.For if we remember these things, we will be able to recognize more easily those things that are said about the diverse nations in the Scriptures. For example, as when it is said that Moses took as his wife the daughter of Jethro, priest of Midian, this Midian is found to be a son of Keturah and Abraham. We know therefore that Moses' wife is from the seed of Abraham and was not a foreigner. But also when it is written, "the queen of Kedar," it should be known no less that also Kedar descends from the very stock of Kedar and Abraham.”

Imported from an open dataset — not yet checked against the printed edition.