It is narrated from Imam Sadeq (AS) who said: Swear to God, Ali Ibn Abitaleb whilst he was alive, never ate Haram and whenever he was faced with two ways which both were for the satisfaction God, he never chose the easy option, and in any important event which occurred for the Prophet (PBUH), because he trusted Imam Ali (AS), the Prophet (PBUH) used to ask him for help.
Among this Ummah (Islamic Ummah) no one was able to follow the way of the Prophet (PBUH) without any diversion like Imam Ali (AS) and despite all that effort, Imam Ali (AS) used to work with fear, one eye towards paradise and the other to the fire, from one side hopeful of rewards of paradise and from the other side, fearful of the torments of fire . It is also narrated by Ibn Abbas who said: In all his works, Imam Ali (AS) was always after Divine satisfaction and that is why he was called “Mortaza” .
 Al-Irshad, Page 255.
 Al-Manaqeb, Vol. 3, Page 110.