(88) باب إِقَامَةِ الصُّلْبِ فِي الرُّكُوعِ
It was narrated that Abu Mas'ud said:
"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.'" (ES)
Reference (ES): Sunan an-Nasa'i 1027 (ES)
In-book reference (ES): Book 11, Hadith 152 (ES)
English translation (ES): Vol. 2, Book 11, Hadith 1028 (ES)