I have to come down on the side of gerard in this. If Allah is the God of Ishmael, then it is the God of Abraham, and therefore the same God who is worshipped by Jews and Christians. One may question the veracity of the alleged revelation to Mahomet, and whether the Muslim notion of God is accurate, but one should remember that according to tradition, Job was not a Hebrew, and nevertheless worshipped God in a satisfactory manner. According to rabbinic tradition, the Noahides, who know God through reason, rather than revelation, and who seek to follow the precepts of morality as best they can, are considered righteous. So it would be the Jewish point of view that Allah was an attempt, at least, to conceive of the true God, and represented an intention to worship Him.
According to Catholic tradition, there is something called "the baptism of desire", which means that if someone is prevented by invincible ignorance from grasping the Gospel, but seeks purity of worship and fidelity to the moral law, doing his best under the dispensation under which he lives, then he is taken to be baptised, and capable of salvation. This has been extended to include those deemed psychologically incapable of breaking from the religion of their fathers, even by some conservative Catholics, like William F. Buckley. On that ground, too, a worshipper of Allah could be deemed someone worshipping the true God through a humanly fallible conception. |