Jews believe in The Satan, and not in the devil.
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.
A FULL EXPLANATION... 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. Other faiths had this same duality:
Greek: Zeus/Hades
Roman: Jupiter/Pluto
Christian: God/Devil
Now, of course, Judaism and the Bible tell of a character called, "The Satan." Every time the term is used in the Hebrew Scriptures, it reads, "HaSaTaN," which means "THE Satan." However, the concept of The Satan is radically different from the idea of the Devil. For Christians, the devil has power and authority in and of himself. However, in the Bible, The Satan only has power granted by God, and has no authority in and of himself. For the devil, or satan, to have power and authority is to have more than one god, as we saw above concerning the Greeks and the Romans.
The Satan is described in only a few places in the Hebrew Scriptures. In every instance, he is an angel who works FOR God, not against God, and must get permission from God for everything that he does. Chronicles, Job, Psalms, and Zechariah are the only places where The Satan is mentioned. In each instance, the job description of The Satan is to act like what we now call a Prosecuting Attorney, or District Attorney, and accuse and show evidence against the defendant. Furthermore, like a D.A., The Satan must obtain permission from God, The Judge, to begin a sting operation.
In the following quotation from the Biblical Book of Job, please take note of who is doing the talking, as The Satan asks God for permission to conduct a sting operation against Job:
And the Eternal said unto <the>Satan, Hast thou considered my servant Job, that there is none like him in the earth, a perfect and an upright man, one that feareth God, and escheweth evil? and still he holdeth fast his integrity, although thou <The Satan> movedst me <God> against him, to destroy him without cause. And Satan answered the Eternal, and said, Skin for skin, yea, all that a man hath will he give for his life. But put forth thine hand <God's hand> now, and touch his bone and his flesh, and he will curse thee to thy face. And the Eternal said unto Satan, Behold, he is in thine hand; but save his life. [Job 2:3-6]
In the above verses, The Satan must get permission from God to perform this "sting operation" on Job. The Satan has no power or authority of his own, like a District Attorney who must also obtain permission from The Judge for anything he does.
Furthermore, the Biblical text paints this same picture of the Satan, when it uses the character of The Satan in what appears to be the end of a court scene. In the following two quotations, The Satan is standing near the accused like the D.A. stands at the end of a court drama on television.
And he shewed me Joshua the high priest standing before the angel of the Eternal, and <the>Satan standing at his right hand to accuse him. And the Eternal said unto Satan, "The Eternal rebuke thee, O Satan; even the Eternal that hath chosen Jerusalem rebuke thee: is not this a brand plucked out of the fire?" [Zechariah 3:1-2]
Set thou a wicked man over him, and let Satan stand at his right hand. When he shall be judged, let him be condemned, and let his prayer become sin. [Psalm 109:6-7]
In the Bible there is also verses which show that it is God, the Creator and Ruler of the whole universe, who is responsible for both the Good and the Bad, and not a devil or god of the underworld:
I am the Eternal, and there is none else, there is no god beside me: I girded thee, though thou hast not known me: That they may know from the rising of the sun, and from the west, that there is none beside me. I am the Eternal, and there is none else. I form the light, and create darkness: I make peace, and create evil: I the Eternal do all these things. [Isaiah 45:5-7]
For God, the Bible, and for Judaism, to have an entity that competes with God, that has power and authority of his own in opposition to God, is to violate the basic idea of monotheism.
What Jews Believe
I personally fought Egyptians. Calling them Muslims indicts all other Muslims into an attachment with this fight. 
