Answer:
Abraham had six other sons besides Ishmael from handmaiden Hagar and Isaac with wife Sarah. He married Keturah after Sarah died. "Now Abraham took another wife, whose name was Keturah. And she bore to him Zimran and Jokshan and Medan and Midian and Ishbak and Shuah," (Gen. 25:1-2).
So he had a total of 8 sons.