Musnad Ahmad 30:2073

Abu al-Ala narrated to us, saying: Layth narrated to us, from Khalid ibn Yazid, from Sa’id ibn Abi Hilal, from Nu’aym al-Mujmir, that he said: I climbed with Abu Hurayrah onto the roof of the mosque, and he was wearing trousers under his shirt. He took off his trousers, then performed ablution and washed his face and his hands, and he extended the ablution up to his upper arms, and his feet, and he extended it up to his shins. Then he said: I heard the Messenger of Allah, may Allah bless him and grant him peace, say: "Indeed, my nation will come on the Day of Resurrection with bright foreheads and bright limbs from the traces of ablution. So whoever among you is able to extend his brightness, let him do so."