3 “They answered and said unto Him, Abraham is our father;” as if, What have you to say against Abraham? Or, If you can, dare to find fault with Abraham. Not that the Lord dared not find fault with Abraham; but Abraham was not one to be found fault with by the Lord, but rather approved. But these men seemed to challenge Him to say some evil of Abraham, and so to have some occasion for doing what they purposed. “Abraham is our father.”
Source: Tractates on the Gospel of John (New Advent)