Musnad Abu Ya'la al-Mawsili 154:18

Muhammad ibn Isma'il ibn Abi Samina al-Basri narrated to us, Mu'tamir narrated to us, he said: I read to Fudayl, from Abu Hurayz, he said: I heard Sa'id ibn Jubayr saying: I heard Ibn 'Umar saying: We were with the Messenger of Allah, may Allah bless him and grant him peace, and we used to consider the fasting of 'Arafah as the fasting of a year.