The Binding of Isaac, in Genesis 22, is a story from the Hebrew Bible in which God asks Abraham to sacrifice his son Isaac on Mount Moriah. To many readers the tale is one of the most challenging, complex, mystifying, and perhaps ethically troublesome episodes in the entire Bible. The story is referred to as the Akedah or Akedat Yitschak (עקידת יצחק) in Hebrew (the binding of Isaac) and as the Dhabih in Arabic.
Abraham agrees to God's command without argument, even though God gives him no reason for the sacrifice (called an Olah in Hebrew -- for the significance of sacrifices, especially in Biblical times, see the korbanot). The text of the story says that God wishes to test Abraham, which indicates that he does not intend for Abraham to actually sacrifice his son. Indeed, after Isaac is bound to an altar, an angel stops Abraham at the last minute, at which point Abraham discovers a ram caught in some nearby bushes. Abraham then sacrifices the ram in Isaac's stead.
According to Josephus, Isaac is twenty-five years old at the time of the sacrifice, while the Talmudic sages teach that Isaac is thirty-seven. In either case, Isaac is a fully grown man, strong enough to prevent the elderly Abraham (who is 125 or 137 years old) from tying him up had he wanted to resist.