Musnad Abu Ya'la al-Mawsili 19:1

Ahmad ibn Isa narrated to us, Ibn Wahb narrated to us, Ibn Lahi'ah narrated to me, from Zabban ibn Fa'id, that Lahi'ah ibn Uqbah narrated to him, from Amr ibn Rabi'ah, from Salamah ibn Qaysar, that the Messenger of Allah (may Allah bless him and grant him peace) said: "Whoever fasts one day seeking the Face of Allah, Allah will distance him from Hell as the distance of a crow that flew while it was a fledgling until it died of old age."