Abu Hazim (may Allah have mercy on him) said: I was behind Sayyiduna Abu Hurayrah (may Allah be pleased with him) while he was performing ablution for prayer. During the ablution he would extend his arm until he reached his armpit. I said to him: O Abu Hurayrah, what kind of ablution is this? He said: O Banu Farrukh, you are here? Had I known that you were here, I would not have performed this ablution. I heard my beloved friend (peace and blessings be upon him) say: "The brightness of the believer will reach as far as the water of ablution reaches."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 257
Sayyiduna Abu Hurayrah (may Allah be pleased with him) said: I heard the Messenger of Allah (peace and blessings be upon him) (and he narrated) the previous hadith.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 258
It is narrated from Nu'aym bin Abdullah al-Mujmir that he said: One day I went up with Sayyiduna Abu Hurayrah (may Allah be pleased with him) onto the roof of the mosque. He was wearing trousers under his shirt. He pulled off his trousers, then performed ablution: he washed his face and his hands, washing his arms up to the shoulders and his feet up to the shins. Then he said: I heard the Messenger of Allah (peace and blessings be upon him) say: "Indeed, my Ummah will come on the Day of Resurrection with the limbs of ablution shining. So whoever among you is able to extend his brightness, let him do so."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 259