'A'isha reported that the Messenger of Allah (ﷺ) would pray in the night for a long time, and when he prayed standing be bowed in a standing posture, and when he prayed sitting, he bowed in a sitting posture.
The Book of Prayer - Travellers
Sahih Muslim 730 b
Hadith Text
'A'isha reported that the Messenger of Allah (ﷺ) would pray in the night for a long time, and when he prayed standing he bowed in a standing posture, and when he prayed sitting, he bowed in a sitting posture.
Commentary
This noble hadith demonstrates the perfection of the Prophet's prayer and his adherence to proper form in all circumstances. When performing voluntary night prayers (Tahajjud), the Messenger of Allah would maintain consistency between his standing and bowing positions. If he began prayer standing due to ability, he would complete his bowing while standing. If physical condition necessitated praying while seated, he would bow while seated.
This teaching establishes that the posture of ruku' should correspond to the posture of qiyam (standing) in the prayer. The wisdom behind this is to maintain the proper structure and reverence of prayer, ensuring each position is performed with stability and devotion. It also shows the Prophet's consideration for his advancing age or any physical limitations while maintaining the integrity of worship.
Scholars derive from this that one who prays sitting due to legitimate excuse should bow while sitting, and one who prays standing should bow while standing. This preserves the natural sequence and dignity of the prayer positions as ordained by Islamic law.