Usul al-Kafi
Book 5:
The Book of Belief and Disbelief

Chapter 14
The reward of the hereafter

628. 1. Imam Jafar as-Sadiq (p): …The reward of any good deed finally depends on belief.(B5,C14,T1)

629. 2. Imam Jafar as-Sadiq (p): Belief is the declaration of faith and acting according to its tenets while Islam is mere declaration without action.(B5,C14,T2)

630. 3. Imam Jafar as-Sadiq (p) was requested to explain the verse: The Bedouins say: ‘We believe.’ Say: ‘You believe not’, but say, ‘We submit’ and faith has not yet entered into your hearts … (Q, 49:14).
The Imam (p): Do you not see that belief is different from faith (submission)?(B5,C14,T3)

631. 4. Imam Jafar as-Sadiq (p) was requested to explain the difference between ‘Belief’ and ‘Islam.’
The Imam (p): ‘Islam’ is just a formal appearance of a person, namely, he bears witness to the oneness of God and that Prophet Muhammad (p) is His prophet, to offer the prescribed prayers, to pay Zakat, and to observe fast during the month of Ramazan, this is Islam. While ‘belief’ is to acknowledge the Principle of Imamate, one who does not believe in Imamate has gone astray.(B5,C14,T4)