"Umar bin Al-Khattab said to us: 'The knees are the Sunnah for you, so hold the knees.'"
Jami` at-Tirmidhi Book 2, Hadith 110
← Previous Hadith Abdullah bin Mas'ud said: "Shall I not demonstrate the Salat of Allah's Messenger to you?" Then he offered Salat and he did not raise his hands except while saying the first Takbir."

Jami` at-Tirmidhi Book 2, Hadith 109 Next Hadith → "We would do that, but then we were prohibited from it, and we were ordered to put our hands on our knees."

Jami` at-Tirmidhi Book 2, Hadith 111