Sunan Abu Dawud
889
Sahih+3

Narrated Abdullah ibn Abbas: Ibn Abbas reported the Prophet (ﷺ) as saying: I have been commanded - according to the version of Hammad: Your Prophet (ﷺ) was commanded - to prostrate on seven (bones), and not to fold back the hair or the clothing

SahihAl-Albani
SahihMuhammad Muhyi Al-Din Abdul Hamid