“The Messenger of Allah ﷺ said: ‘No prayer is acceptable in which a man does not settle his spine when bowing and when prostrating.’” (Using translation from Ibn Mājah 870)
قَالَ رَسُولُ اللهِ ﷺ لَا يُجْزِي صَلَاةٌ لَا يُقِيمُ الرَّجُلُ صُلْبَهُ فِي الرُّكُوعِ وَالسُّجُودِ