Musnad Ahmad 30:2632

Waki' narrated to us, he said: Hawshab ibn 'Aqil narrated to me, he said: Mahdi al-'Abdi narrated to me, from 'Ikrimah, he said: I entered upon Abu Hurayrah in his house, and I asked him about fasting the day of 'Arafah while at 'Arafat. Abu Hurayrah said: "The Messenger of Allah, may Allah bless him and grant him peace, forbade fasting the day of 'Arafah while at 'Arafat."