'Only Son' in the Bible

He said, "Now take your son, your only son, whom you love, even Isaac, and go into the land of Moriah. Offer him there for a burnt offering on one of the mountains which I will tell you of."

He said, "Do not lay your hand on the boy, neither do anything to him. For now I know that you fear God, seeing you have not withheld your son, your only son, from me."

and said, "I have sworn by myself, says the LORD, because you have done this thing, and have not withheld your son, your only son,