Adam Clarke on Numbers 22:5

To Pethor, which is by the river of the land of the children of his people - Dr. Kennicott justly remarks, that "the description now given of Balaam's residence, instead of being particular, agrees with any place in any country where there is a river; for he lived by Pethor, which is by the river of the land of the children of his people. But was Pethor then near the Nile in Egypt? Or in Canaan, near Jordan? Or in Mesopotamia, near the Euphrates, and belonging to the Ammonites? This last was in fact the case; and therefore it is well that twelve Hebrew MSS. (with two of De Rossi's) confirm the Samaritan text here in reading, instead of עמו ammo, his people, עמון Ammon, with the Syriac and Vulgate versions." Houbigant properly contends for this reading; and necessity urges the propriety of adopting it. It should therefore stand thus: by the river of the land of the children of Ammon; and thus it agrees with Deu 23:4.