What was the first prayer in which the Messenger of Allah, may Allah bless him and grant him peace, bowed?

Some scholars have mentioned that the first prayer the Prophet, peace and blessings be upon him, prayed with bowing (ruku'), was the Asr prayer after the Isra' and Mi'raj. Al-Suyuti argued that the Prophet, peace and blessings be upon him, prayed the Dhuhr prayer on the morning of the Isra' without bowing, and that the night prayers before that were also without bowing, which indicates that bowing is specific to this Ummah. A weak hadith to this effect has been narrated from Ali, may Allah be pleased with him.