Musannaf Ibn Abi Shayba 1:176

176. Ibn Numayr narrated to us, from ‘Abd al-Malik ibn Sulaym, from ‘Abd Khayr, who said: We were with ‘Ali one day at the morning prayer. When he finished, he called the servant for a basin, and he performed ablution. Then he inserted his two fingers into his ears, and then he said to us: "This is how I saw the Messenger of Allah, may Allah bless him and grant him peace, perform ablution."