Musannaf Ibn Abi Shayba 1:42

Yahya ibn Zakariyya ibn Abi Za'idah narrated to us, from Abu Malik al-Ashja'i, from Abu Hazim, from Abu Hurayrah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "You will come to me with white foreheads and white limbs from the traces of ablution; a mark of my nation that no one else possesses."