Assalamu'alaikum, I read that to bow down in prayer, one's back must be at the same level as his head. But my backbone stays a bit high. Can I fold my hands to lean down a little bit more, or my hands should stay straight, like a rod? can you tell me what to do minimum while bowing down so that my prayer remains valid? Jazakallah khairan.

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

The Rukoo’ (bowing down in prayer) that is sufficient in prayer is for the worshiper to bow down to the extent that his hands can touch his knees, and it is not a condition for its validity that the back should be straight.

As for the most complete Rukoo’, and what is desirable in it, it is for the worshiper to put his hands on his knees, his fingers spread apart, straighten his back, put his head straight (at the same level) as his back, and keep his upper arms and sides wide open.

Therefore, if you do the complete Rukoo’, then this is better but if you did not do so and bowed down to the extent that your hands touch your knees while observing Tuma’neenah, then your prayer is valid and you do not have to do anything because you have fulfilled the sufficient Rukoo’.

Tuma’neenah means that each body part settles in its place for the least time possible before one moves from one position to another.

For more benefit on observing Tuma'neenah in prayer, please refer to Fataawa 180233, 200531, 350416, 338716, 391381, and 326782.

Allah knows best.