Musnad Ahmad 5:750

'Abdullah narrated to us, 'Abd al-Rahman ibn 'Umar narrated to me, Abu Mu'awiyah narrated to us, from 'Abd al-Rahman ibn Ishaq al-Qurashi, from Sayyar Abu al-Hakam, from Abu Wa'il, who said: A man came to 'Ali, may Allah be pleased with him, and said: "O Commander of the Faithful, I have become unable to fulfill my *kitabah* (contract of manumission), so help me." 'Ali, may Allah be pleased with him, said: "Shall I not teach you words that the Messenger of Allah, may Allah bless him and grant him peace, taught me? If you had a debt like the mountain of Sir in gold, Allah would pay it off for you." I said: "Yes." He said: "Say: 'O Allah, suffice me with Your lawful against Your prohibited, and enrich me by Your bounty over those other than You.'"