IN SHORT... For Jews, anything that even remotely conflicts with the idea that God is One and Indivisible will be rejected because it precludes true, pure, monotheism. The idea that there is a God in heaven above who fights against a god of the underworld, or hell, is not monotheism, however, it is the same duality found in other pagan faiths. The Bible speaks of a character known as The Satan, who acts like a prosecuting attorney, or a district attorney, in God's court. However, The Satan has no power or authority in and of himself, rather he must get permission from the Judge, God, to do anything
Muslims believe in the same oneness of God (At-Tauhid is the Arabic term) and that all beings, Satan included, are at the mercy and obedience of the one true God (Allah is just the Arabic term for God). To associate anything or anyone with God or to share worship with anyone other than God, including Jesus, is a major sin.