(54) باب إِقَامَةِ الصُّلْبِ فِي السُّجُودِ
It was narrated that Abu Mas'ud said:
"The Messenger of Allah (ﷺ) said: 'No prayer is valid in which a man does not maintain his back (at ease) when bowing and prostrating.'" (ES)
Reference (ES): Sunan an-Nasa'i 1111 (ES)
In-book reference (ES): Book 12, Hadith 83 (ES)
English translation (ES): Vol. 2, Book 12, Hadith 1112 (ES)