مُسْنَدُ أَحْمَدَ
Musnad Ahmad 3075
Musnad of 'Abdullah bin al-'Abbas bin 'Abdul-Muttalib from the Prophet
It was narrated that ‘Ikrimah said: I saw a man praying in the Mosque of the Prophet (ﷺ). He said takbeer when he prostrated, when he got up and when he went down. I found that strange and I mentioned it to Ibn 'Abbas (رضي الله عنه) He said: May you be bereft of your mother! That is the prayer of the Messenger of Allah (ﷺ).
Musnad Ahmad 3101lts isnad is saheeh]