John Gill Commentary Genesis 22:20

"And it came to pass after these things, that it was told Abraham, saying, Behold, Milcah, she also hath borne children unto they brother Nahor." — Genesis 22:20 (ASV)

And it came to pass, after these things Abraham's taking his son Isaac to the land of Moriah, building an altar on one of the mountains there, and laying him on it with an intention to sacrifice him, and offering of a ram in his stead, and the return of them both to Beersheba:

that it was told Abraham; by some person very probably who was lately come from those parts where the following persons lived; though Jarchi suggests this was told him by the Lord himself, and while he was thinking of taking a wife for Isaac of the daughters at Aner, or Eshcol, or Mamre; and to prevent which the following narration was given him:

saying, behold Milcah, she has also borne children unto your brotherNahor; as Sarah, supposed to be the same with Iscah, a daughter of Haran, had borne a son to him, and whom he had received again as from the dead; so Milcah, another daughter of Harsh, had borne children to his brother Nahor, whom he had left in Ur of the Chaldees, when he departed from thence, and who afterwards came and dwelt in Haran of Mesopotamia; see (Genesis 11:27Genesis 11:29) .