Genesis 21:10

“Wherefore she said unto Abraham, cast out this bondwoman and her son, etc.] 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 plainly that there would be no peace nor comfort for her and her son, unless Hagar and her son were turned out of doors, for which she moves Abraham; and this not merely in a passion, but by divine direction and influence, as is evident from God’s approbation of it: for the son of this bondwoman shall not be heir with my son,…”

“Wherefore she said unto Abraham, Cast out this bondwoman--Nothing but the expulsion of both could now preserve harmony in the household. Abraham's perplexity was relieved by an announcement of the divine will, which in everything, however painful to flesh and blood, all who fear God and are walking in His ways will, like him, promptly obey. This story, as the apostle tells us, in "an allegory" [Gal 4:24], and the "persecution" by the son of the Egyptian was the commencement of the four hundred years' affliction of Abraham's seed by the Egyptians.”

“21:10 Earlier, Sarah mistreated Hagar and pressured her to flee (16:6); when Hagar’s son mistreated Isaac, Sarah demanded that that slave woman and her son leave.”