The Qur'an (Sura Nisaa verses 150-152) teaches the following on the subject of discrimination:
"Those who deny God and His apostles and wish to separate God from His apostles, saying 'We believe in some but reject others,' and wish to take a course midway, they are in truth unbelievers; and we have prepared a humiliating punishment for unbelievers. To those who believe in God and His apostles and make no distinction between any of the apostles, we shall soon give their rewards: for God is oft-forgiving, most merciful."
We see several interesting things in the above verses. They report that those who say of God's apostles: 'We believe in some, but reject others,' are actually unbelievers (that is, kafir), and that a severe punishment will be their reward. On the other hand, those who make no distinction between God's apostles, according to the above verses, will receive a good reward.
Unfortunately, discrimination regarding God's prophets, though spoken of here as a trait of the unbelievers (kafirun), is widely practiced in Islam. One need go no further than the Shahada before one is confronted with it. "There is no god but God and Muhammad is the messenger of God." In Islam, Abraham, Moses, David and Jesus are also the messengers of God, but they are allowed no place in the Shahada!
The Qur'an itself acknowledges that the Holy Tawrat, Zabur and Injil are also Allah's Word, but since Muslims distinguish Muhammad as greater than Moses, David and Jesus, only the Qur'an is read. If there were no discrimination in Islam, the Holy Tawrat, Zabur and Injil would also be read and made available in mosques.
According to the Qur'an, those who distinguish one prophet greater than another are unbelievers, that is kafir, and their punishment will be great.