Musnad Abu Ya'la al-Mawsili 3:348

Abu Khaythama narrated to us, Marwan bin Mu'awiyah al-Fazari narrated to us, Azhar bin Rashid al-Kahili narrated to us, from al-Khidr bin al-Qawas al-Bajali, from Abu Sakhila, who said: Ali said: "Shall I not inform you of the best verse in the Book of Allah, which the Messenger of Allah (peace and blessings of Allah be upon him) narrated to us? 'And whatever strikes you of disaster - it is for what your hands have earned; but He pardons much' (Ash-Shura: 30)." He said: "And he said: 'I will explain it to you, O Ali: Whatever strikes you of illness, punishment, or affliction in the world, it is for what your hands have earned. And Allah is too Generous to punish you twice for the same thing in the Hereafter. And whatever Allah has pardoned in the world, Allah is too Majestic to return to it after His pardon.'"