Charles Ellicott Commentary Numbers 23:19

"God is not a man, that he should lie, Neither the son of man, that he should repent: Hath he said, and will he not do it? Or hath he spoken, and will he not make it good?" — Numbers 23:19 (ASV)

Neither the son of man, that he should repent.— The adoption of these words, with slight variation, by Samuel (1 Samuel 15:29) provides evidence of his familiarity with this portion of the Pentateuch.