Musnad Ahmad 5:689

Abu Nu'aym narrated to us, Sharik narrated to us, from al-Aswad ibn Qays, from 'Amr ibn Sufyan, who said: A man delivered a sermon on the day of Basra, when Ali appeared. Ali said: "This eloquent orator has preceded the Messenger of Allah, may Allah bless him and grant him peace, and Abu Bakr prayed, and Umar made it three. Then a tribulation struck us after them, in which Allah does what He wills."