مُسْنَدُ أَحْمَدَ
Musnad Ahmad 2424
Musnad of 'Abdullah bin al-'Abbas bin 'Abdul-Muttalib from the Prophet
It was narrated that Ibn 'Abbas (رضي الله عنه) said: The Prophet (ﷺ) was commanded to prostrate on seven and not to tuck up his hair or garment.
Musnad Ahmad 2436lts isnad is saheeh, al-Bukhari (809) and Muslim (490)]