"The Messenger of Allah ﷺ said: 'The prayer is not valid if a man does not bring his backbone to rest while bowing and prostrating.'"  

قَالَ رَسُولُ اللَّهِ ﷺ لاَ تُجْزِئُ صَلاَةٌ لاَ يُقِيمُ الرَّجُلُ فِيهَا صُلْبَهُ فِي الرُّكُوعِ وَالسُّجُودِ