Musannaf Ibn Abi Shayba 1:399

Narrated to us Abd al-Rahim ibn Sulayman, from Abd al-Malik ibn Sula', from Abd Khayr, who said: We were with Ali one day at the morning prayer. When he finished, he called the servant for the basin, and he performed ablution. Then he inserted his two fingers into his ears, and then said: "Thus I saw the Messenger of Allah, may Allah bless him and grant him peace, perform ablution."