"shalt call his name Isaac: and I will establish My covenant with him.” Yet God was not unmindful of the father's prayer. “As for Ishmael,” He said, “I have heard thee: Behold, I have blessed him, ... and I will make him a great nation.” PP 146.1"
"And God said, Sarah thy wife shall bear thee a son indeed; and thou shalt call his name Isaac: and I will establish my covenant with him for an everlasting covenant, and with his seed after him."
The EGW passage directly quotes and references Genesis 17:19.
"And as for Ishmael, I have heard thee: Behold, I have blessed him, and will make him fruitful, and will multiply him exceedingly; twelve princes shall he beget, and I will make him a great nation."
The EGW passage directly quotes and references Genesis 17:20.
The birth of Isaac, bringing, after a lifelong waiting, the fulfillment of their dearest hopes, filled the tents of Abraham and Sarah with gladness. But to Hagar this event was the overthrow of her fondly cherished ambitions. Ishmael, now a youth, had been regarded by all in the encampment as the heir of Abraham's wealth and the inheritor of the blessings promised to his descendants. Now he was suddenly set aside; and in their disappointment, mother and son hated the child of Sarah. The general rejoicing increased their jealousy, until Ishmael dared openly to mock the heir of God's promise. Sarah saw in Ishmael's turbulent disposition a perpetual source of discord, and she appealed to Abraham, urging that Hagar and Ishmael be sent away from the encampment. The patriarch was thrown into great distress. How could he banish Ishmael his son, still dearly beloved? In his perplexity he pleaded for divine guidance. The Lord, through a holy angel, directed him to grant Sarah's desire; his love…
"And Sarah saw the son of Hagar the Egyptian, which she had born unto Abraham, mocking."
The EGW passage directly recounts the event described in Genesis 21:9, where Sarah sees Ishmael mocking Isaac.