(2) باب الإِمْسَاكِ بِالرُّكَبِ فِي الرُّكُوعِ
It was narrated that 'Umar said:
"It is established for you to hold the knees, so hold the knees."
Reference: Sunan an-Nasa'i 1034
In-book reference: Book 12, Hadith 6
English translation: Vol. 2, Book 12, Hadith 1035