He discovered his father's plan after he asked where the lamb was for the burnt offering
... And Isaac spake unto Abraham his father, and said, My father: and he said, ... 
Isaac asked, "The fire and the wood are here, but where's the lamb for the .... 
Genesis 22:1 And it came to pass after these things, that God did tempt Abraham, 
 [DOC] [TLE] Genesis 22:8 Abraham answered, "God himself will provide the ... [PAR] Abraham said, God will provide for himself the lamb for a burnt offering, my son.