Sahih Muslim Book 1, Hadith Number 148.

Chapter : Belief in Allah is the best of deeds.

Abu Huraira reported: The Messenger of Allah was asked about the best of deeds. He observed: Belief in Allah. He (the inquirer) said: What next? He (the Holy Prophet) replied: Jihad (struggle to the utmost) in the cause of Allah. He (the inquirer) again said: What next? He (the Holy Prophet) replied: Pilgrimage accepted into the grace of the Lord. In the tradition narrated on the authority of Muhammad b. Ja’far (the words are) that he (the Holy Prophet) said: Belief in Allah and His Messenger. Muhammad b. Rafi and ‘Abd b. Humaid, ‘Abdur-Razzaq and Ma’mar and Zuhri have narrated a hadith like this on the authority of the same chain of transmitters.