Jami At Tirmidhi
258
Sahih Isnaad+3

Abu Abdur-Rahman As-Sulami said:"Umar bin Al-Khattab [may Allah be pleased with him] said to us: 'The knees are the Sunnah for you, so hold the knees

Sahih IsnaadAhmad Muhammad Shakir
Sahih IsnaadAl-Albani