Musnad Ahmad 31:222

Ibn Numayr narrated to us, Sufyan narrated to us, from Sumayy, from al-Nu’man ibn Abi ‘Ayyash al-Zuraqi, from Abu Sa’id al-Khudri, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "No servant fasts a day in the way of Allah, except that Allah distances the Fire from his face by that day [a distance of] seventy autumns."