Musnad Ahmad 790:67

'Abd al-Wahhab narrated to us, Khalid narrated to us, from a man, from Mutarrif ibn al-Shikhkhir, from 'Imran ibn Husayn, who said: "I prayed behind 'Ali ibn Abi Talib a prayer that reminded me of a prayer I had prayed with the Messenger of Allah (may Allah bless him and grant him peace) and the two Caliphs." He said: "So I went and prayed with him, and he would say the takbir whenever he prostrated and whenever he raised his head from bowing." I said: "O Abu Nujayd, who was the first to abandon it?" He said: "'Uthman ibn 'Affan; when he grew old and his voice became weak, he abandoned it."