Differing grades
No. 1026
"Shall I not tell you about the prayer of the Messenger of Allah (ﷺ)? He stood and raised his hands the first time and then he did not do that again."
فَقَامَ فَرَفَعَ يَدَيْهِ أَوَّلَ مَرَّةٍ ثُمَّ لَمْ يُعِدْ .
Sunan an-Nasa'iBook 11
The Book of the Commencement of the PrayerPage 4
كتاب الافتتاح
153 hadith in this book; 153 translated into English.
Chapter 87Chapter: Not doing that
Chapter 88Chapter: Bringing one's backbone to rest when bowing
Authentic
No. 1027
"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.'"
" لاَ تُجْزِئُ صَلاَةٌ لاَ يُقِيمُ الرَّجُلُ فِيهَا صُلْبَهُ فِي الرُّكُوعِ وَالسُّجُودِ "
Chapter 89Chapter: Being moderate in bowing
Authentic
Muttafaq ‘alayh (Bukhari and Muslim) No. 1028
"Be moderate in bowing and prostration, and do not rest your forearms along the ground like a dog."
" اعْتَدِلُوا فِي الرُّكُوعِ وَالسُّجُودِ وَلاَ يَبْسُطْ أَحَدُكُمْ ذِرَاعَيْهِ كَالْكَلْبِ "