How then shall they call on Him in Whom they have not believed ?
And how shall they believe in Him of Whom they have not heard ?
And how shall they hear without a preacher ?
So, the faith comes by hearing and hearing by the word of God.
Say ye: “We believe in Allah (God), and the revelation given to us, and to Abraham, Isma’il, Isaac, Jacob, and the Tribes, and that given to Moses and Jesus, and that given to (all) prophets from their Lord: We make no difference between one and another of them: And we bow to Allah (Quran 2:136)
The Messenger believeth in what hath been revealed to him from his Lord, as do the men of faith. Each one (of them) believeth in Allah, His angels, His books, and His apostles. “We make no distinction (they say) between one and another of His apostles.” And they say: “We hear, and we obey: (We seek) Thy forgiveness, our Lord, and to Thee is the end of all journeys.” (Quran 2:285)
The desert Arabs say, “We believe.” Say, “Ye have no faith; but ye (only)say, ‘We have submitted our wills to Allah,’ For not yet has Faith entered your hearts. But if ye obey Allah and His Messenger, He will not belittle aught of your deeds: for Allah is Oft-Forgiving, Most Merciful.” Only those are Believers who have believed in Allah and His Messenger, and have never since doubted, but have striven with their belongings and their persons in the Cause of Allah: Such are the sincere ones. (Quran 49:14&15)