Sunan Abu Dawud
845
Sahih+3

Tawus said:we asked Ibn ‘Abbas about sitting on heels between the two prostrations. He said: It is the sunnah. We said: We look upon it as a pressure on the foot. He said: This is the sunnah of your Prophet(ﷺ)

SahihAl-Albani
SahihMuhammad Muhyi Al-Din Abdul Hamid