Questions and Answers on Islamic Doctrine
Chapter 2: Belief in Prophets and Missions
Question 10: In what way was Jesus Christ a Muslim, as well as all the other prophets?
Answer 10: There is no doubt that all prophets (peace be upon them), beginning with Adam and ending in Muhammad, preached one religion—the worship of God alone and disregarding all other powers. This is something advocated by Islam. God says: “Truly, the true religion with God is Islam” (Holy Qur’an: 3: 19). About Abraham (pbuh), God says: “Abraham was neither a Jew nor a Christian, but was a true Muslim (hanif: monotheist—a worshipper of God alone) and he was not a mushrik—a polytheist” (Holy Qur’an: 3: 67). On the question of the disciples of Jesus, God says: “And when I (God) inspired al-hawariun (the disciples of Jesus) to believe in Me and My Messenger, they said: ‘We believe. And bear witness that we are Muslims’.” (Holy Qur’an: 5: 111). Prophet Muhammad (pbuh) confirmed this in his saying: “Prophets are paternal brothers; their mothers are different, but their religion is one.”
 Cited in Bukhalri, Hadith No. 1437.