Musannaf Ibn Abi Shayba 3:1349

Abu Bakr narrated to us, he said: Abd al-A’la narrated to us, from his uncle, from al-Zuhri, from Ubayd Allah ibn Rafi’, from Ali, that he used to say: The Imam and those behind him recite in the Dhuhr and the Asr, in the first two rak'ahs, the Opening of the Book (al-Fatiha) and a surah. And in the last two, they recite the Opening of the Book.