But Sarah saw that the son whom Hagar the Egyptian had borne to Abraham was mocking her son,
9. And Sarah saw the son of Hagar . As the verb to laugh has a twofold signification among the Latins, so also the Hebrews use, both in a good and evil sense, the verb from which the participle מצחק ( metsachaik ) is derived. That it was not a childish and innoxious laughter, appears from the indignation of Sarah.
The casting out of Ishmael is here considered of, and resolved on. I. Ishmael himself gave the occasion by some affronts he gave to Isaac his little brother, some think on the day that Abraham made the feast for joy that Isaac was safely weaned, which the Jews say was not till he was three years old, others say five.
Commenting on Genesis 21:9-13
Wherefore she said unto Abraham, cast out this bondwoman and her son,.... Hagar, Sarah's handmaid and bondservant, and her son Ishmael; by this it appears that Hagar was concerned in this affair, and set her son on to mock Isaac, at least she encouraged him in it, buoying: him up with his being the firstborn, and having a right to the inheritance; wherefore Sarah saw...