Isaac.

Genesis 17:19-21
But God replied, "Your wife Sarah will indeed bear you a son, and you are to name him Isaac. I will establish My covenant with him as an everlasting covenant for his descendants after him. . . .

Genesis 21:2-5, 12
So Sarah conceived and bore a son to Abraham in his old age, at the very time God had promised him. . . .

Ishmael.

Genesis 16:11-16
The Angel of the LORD proceeded: "Behold, you have conceived and will bear a son. And you shall name him Ishmael, for the LORD has heard your cry of affliction. . . .

Genesis 21:9, 10
But Sarah saw that the son whom Hagar the Egyptian had borne to Abraham was mocking her son, . . .