Some argue that the Bible is contradictory concerning how many sons Abraham had, whether he had one or two. The argument is that Genesis 22:2 and Hebrews 11:17 say that Abraham had one child, but Galatians 4:22 says that Abraham had two children. However, the solution to this alleged contradiction is extremely simple.
He said, “Take your son, your only son Isaac, whom you love, and go to the land of Moriah, and offer him there as a burnt offering on one of the mountains of which I shall tell you.”
Genesis 22:2
By faith Abraham, when he was tested, offered up Isaac, and he who had received the promises was in the act of offering up his only son,
Hebrews 11:17
For it is written that Abraham had two sons, one by a slave woman and one by a free woman.
Galatians 4:22
Abraham obviously had two sons. Genesis itself records the birth of two sons, Ishmael and Isaac, so we should assume the author would not contradict himself in Genesis 22:2.
When the Bible says that Abraham only had one son, it is saying that he only had one ”’promised”’ son. This was Isaac, the son of whom Jesus would be an eventual offspring.
There are some foundational principles that apply to all alleged and apparent contradictions in the Bible. To read more, see Bible Difficulties: Foundational Principles.
To read more answers to alleged and apparent contradictions in the Bible, see “Contradictions” in the Bible Answered.
These books are also excellent resources:
Evidence That Demands a Verdict: Life-Changing Truth for a Skeptical World - Josh and Sean McDowell
Little Pilgrim's Progress (Illustrated Edition) - Helen L. Taylor