The Rukūʿ of the Messenger (صلى الله عليه وسلم) Shaykh Muḥammad ibn ʿUmar Bāzmūl Taken From the Book: Sharḥ Ṣifah Ṣalāt al-Nabī’ (Explanation of the Prophet’s Prayer Described) [currently being translated].
What is the description of the rukūʿ? The description of the rukūʿ is that the individual bends his back and places his hands upon his knees; his back is to be level to the point that if a person were to come with a hollow plate and place it upon his back it would remain in its place. So this indicates that the back is level.
The author (Shaykh al-Albānī), may Allāh have mercy upon him, has mentioned in that which he has cited from the aḥadīth, that the Messenger (صلى الله عليه وسلم), when he would bow, would spread his back to the point that if someone were to pour water upon it then it would remain in its place. Because then the back is level and is not curved (or bent). As for the head and the neck, then he would not droop his head, meaning he would not bend it towards the ground. Nor would he raise it, meaning he would not raise it higher than the level of his back. And he is to place his head and neck even with the level of his back. What is affirmed, as the author has mentioned, in the aḥadīth, is that the Messenger (صلى الله عليه وسلم) would place his palms upon his knees. Not upon his thighs above the knees. Nor upon the shin below the knees. He would separate his fingers and firmly grasp his knees with his hands as if he holding his knees.
Translated by Raha Batts