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

Chapter 11
Purity of faith

619. 1. Imam Jafar as-Sadiq (p) was requested to explain the term Hanifan Muslima (an upright Muslim) (Q, 3:67).
The Imam (p): An upright Muslim is one who sincerely worships God without the slightest trace of idolatry.(B5,C11,T1)

620. 3. Imam Ali ar-Reza (p) quoted Imam Ali (p): Give glad tidings to the one who worships and prays to God sincerely. Whatever he sees, it does not divert his attention from God. Whatever he hears, it does not make him forget God and whenever he gives something to others he is not saddened.(B5,C11,T3)

621. 4. Imam Jafar as-Sadiq (p): God tests you to see which one of you is best in his good deeds. Goodness of deeds does not depend on its quantity, but on the truth of the deed, the fear of God and the sincerity of purpose. To remain sincere while performing a good deed is harder than its performance. The sign of a good deed is that you should not expect any praise for it…(B5,C11,T4)

622. 5. Imam Jafar as-Sadiq (p) was requested to comment on the verse: Save him who comes to God with a submissive heart (Q, 26:89).
The Imam (p): A submissive heart has no one in it except God. Any heart with a trace of polytheism or doubt deserves outright rejection.(B5,C11,T5)

623. 6. Imam Muhammad al-Baqir (p): Anyone who remains absolutely sincere in his faith in God continuously for forty days and remembers Him for forty days, God will make this world repulsive in his eyes and will fill his heart and speech with wisdom …(B5,C11,T6)