They were talking about DIFFERENT Abrahams.
The Muslims worship Abraham Ahmed's God.
The Jews/Christians worship Abraham Goldstein's God.
That must be it, right, sandy?
If you think Jesus was referring to Abraham's God from the Old Testament (Tanakh) when he referred to his father, then you are talking about the same God.
How interpretations and impressions of that God may have changed after the fact, based on the different prophets (as they did with each Patriarch) does not change the fact that all three Abrahamic religions (ever wonder where they got that term?) all worship Abraham's God.
Muslims, sandy, are your brothers and sisters, regardless of how deep your fingers are in your ears, and how loudly you scream.