Musannaf Ibn Abi Shayba 3:1993

Ubayd Allah narrated to us, he said: Isra'il informed us, from Abu Ishaq, from 'Amr ibn Maymun, from al-Rabi' ibn Khuthaym, who said: "If the prostration (sajdah) is at the end of the surah, then if you wish, bow (ruku'), and if you wish, prostrate (sujud); for the bowing is with the prostration."