Sayyidah Aisha (may Allah be pleased with her) says that when the Messenger of Allah (peace and blessings be upon him) performed prayer standing, he would also perform the bowing (ruku') standing, and when he performed prayer sitting, he would also perform the bowing sitting.
Hadith Referenceالفتح الربانی / أبواب صلاة السفر وآدابه وأذكاره وما يتعلق به / 2438
Hadith Gradingمحدثین:أخرجه مسلم: 730
Hadith Takhrij«أخرجه مسلم: 730 ، (انظر مسند أحمد ترقيم الرسالة: 24019، 24822 ترقیم بيت الأفكار الدولية: 25320»