مُسْنَدُ أَحْمَدَ
Musnad Ahmad 3435
Musnad of 'Abdullah bin al-'Abbas bin 'Abdul-Muttalib from the Prophet
It was narrated that Ibn ‘Abbas (رضي الله عنه) said: I was in the house of Maimoonah and the Prophet (ﷺ) got up to pray at night. I got up and stood on his left, and he took me by the hand and made me stand on his right. Then he prayed thirteen rak'ahs and I estimated the length of time he stood in each rak'ah as being as long as it takes to recite Yu ayyuhal-Muzzammil (Soorat al-Muzzammil 73:1)
Musnad Ahmad 3459lts isnad is saheeh]