Musnad Ahmad 1007:101

'Affan narrated to us, Hammam narrated to us, Yahya ibn Abi Kathir narrated to us, 'Abdullah ibn Abi Qatadah narrated to us, from his father: That the Prophet, peace and blessings of Allah be upon him, used to recite in the Dhuhr prayer, in the first two rak'ahs, the Mother of the Book (Al-Fatihah) and two surahs. He would sometimes let us hear the verse. He said: And he used to recite in the last two rak'ahs the Mother of the Qur'an (Al-Fatihah). He said: And he used to prolong the first rak'ah in a way he did not prolong the second. And likewise in the 'Asr prayer, and likewise in the Fajr prayer. 'Affan said: And Aban ibn Yazid al-'Attar [narrated] the like of it, exactly.