مُسْنَدُ أَحْمَدَ
Musnad Ahmad 2250
Musnad of 'Abdullah bin al-'Abbas bin 'Abdul-Muttalib from the Prophet
’Ikrimah, the freed slave of Ibn ‘Abbas (رضي الله عنه) said: I prayed behind Abu Hurairah; when he bowed, and when he prostrated, he said Allahu Akbar. I mentioned that to Ibn 'Abbas and he said: May you have no mother! Isn't that the Sunnah of the Messenger of Allah (ﷺ)?
Musnad Ahmad 2257lts isnad is saheeh]