Abraham had only one son.
Hebrews 11:17
By faith Abraham when he was tried, offered up Isaac, ... his only begotten son.
Genesis 22:2
Take now thy son, thine only son Isaac, ... and offer him there for a burnt offering.
Abraham had more than one son.
Genesis 16:15
And Hagar bare Abraham a son: and Abram called his son's name, which Hagar bare, Ishmael.
Genesis 21:2-3
For Sarah conceived, and bare Abraham a son is his old age .... And Abraham called him Isaac.
Genesis 25:1-2
Then again Abraham took a wife, and her name was Keturah. And she bare him Zimran, and Jokshan, and Medan, and Midian, and Ishbak, and Shuah.
Galatians 4:22
Abraham had two sons; the one by a bond-woman, and the other by a free woman.
This is another simple one, Abraham had a son Ishmael with his slave because sarah was too old. Then he had isaac and God told him that he was the appointed one so he cast him out into the desert. So buy the time he was going to sacrifice Isaac he indeed only had "one" son, because ishmael was in the desert somewhere.
Then is Genesis 25:1-2, that was after all that happened (the near- sacrifice, and the birth of Ishmael) and near Abrahams death.
