Musnad Ahmad 788:14

Yahya—meaning Ibn Adam—narrated to us, Ammar ibn Ruzayq narrated to us, from Abu Ishaq, from Burayd ibn Abi Maryam, from al-Ash’ari, who said: We mentioned Ibn Abi Talib while we were in Basra, "A prayer we used to perform with the Messenger of Allah, may Allah bless him and grant him peace; he would say the takbir when he prostrated and when he stood up." I do not know whether we forgot it or whether we abandoned it intentionally.