(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.'" (ID)
Reference (ID): Sunan an-Nasa'i 1027 (ID)
In-book reference (ID): Book 11, Hadith 152 (ID)
English translation (ID): Vol. 2, Book 11, Hadith 1028 (ID)