Musnad Abu Ya'la al-Mawsili 159:132

Daud ibn 'Amr al-Dabbi narrated to us, Muhammad ibn Muslim al-Ta'ifi narrated to us, from 'Amr ibn Dinar, from 'Ata' ibn Yasar, from Abu Hurayrah, that the Prophet (peace and blessings of Allah be upon him) said: "When the prayer is established, there is no prayer except the obligatory one."