Musnad Ahmad 30:3647

'Abd al-Malik ibn 'Amr narrated to us, Fulayh narrated to us, from Nu'aym ibn 'Abd Allah, that he climbed up to Abu Hurayrah on the roof of the mosque, and found him performing ablution. He raised his arms, then turned to me and said: I heard the Messenger of Allah (peace and blessings of Allah be upon him) say: "Indeed, my nation on the Day of Resurrection will be the *ghurr* (bright-faced) and *muhajjalun* (bright-limbed) due to the traces of ablution." Whoever among you is able to lengthen his brightness, let him do so. I do not know if this is from the speech of the Messenger of Allah (peace and blessings of Allah be upon him) or from the speech of Abu Hurayrah.