صحیح ابن حبان
Ibn Hibban
كتاب الصلاة
Book of Prayer
باب النوافل - ذكر العلة التي من أجلها كان يقوم صلى الله عليه وسلم من قعوده عند إرادة الركوع
Section on voluntary prayers – mentioning the reason why the Prophet would stand from sitting when intending to bow
1 hadith
Hadith 2510
Abdullah bin Shaqiq narrates about Sayyidah Aisha (may Allah be pleased with her): I asked her about the prayer of the Prophet (peace and blessings of Allah be upon him). She said: The Prophet (peace and blessings of Allah be upon him) used to perform long prayers at night while sitting and also used to perform long prayers while standing. When he performed prayer sitting, he would go into bowing (ruku) from the sitting position, and when he performed prayer standing, he would go into bowing from the standing position.