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

Chapter 39
Abstinence from sins

709. 2. Imam Muhammad al-Baqir (p): On the Day of Judgement every eye will be in tears except three:
a. One, who keeps awake during nights worshipping God,
b. Second, who cries due to fear of God, and
c. Third, who abstains from sins.(B5,C39,T2)

710. 4. Imam Jafar as-Sadiq (p): God has enjoined on His believer his remembrance. I do not mean the four familiar glorifications namely: Subhanallah Wal Hamdulillah Wala Ilaha Illallahu Wallahu Akbar. Although, they are also among the remembrances, I mean the remembrance which comes when some permissible act is performed in the hope of reward and the remembrance which comes at the time of abstinence from something which is forbidden due to the fear of God.(B5,C39,T4)

711. 6. Imam Jafar as-Sadiq (p) quoted Prophet Muhammad (p): One who abstains from sins due to fear of God; He will be pleased with him on the Day of Judgement.(B5,C39,T6)