Whenever a man and woman have sex resulting in the birth of a child, they become father and mother of that child. Nothing complicated about that. Therefore at no point during Ishmael's life was Abraham NOT the father of Ishmael. It is crazy for the Bible to suggest that Isaac was Abraham's ONLY son since Ishmael was already some 14 years at the time of Isaac's birth. The Bible suggesting that God said "take your son, your only son, Isaac" means only one of two things. Either the Bible is confused or God is.