مُسْنَدُ أَحْمَدَ
Musnad Ahmad 3444
Musnad of 'Abdullah bin al-'Abbas bin 'Abdul-Muttalib from the Prophet
Abush-Sha'tha' narrated that Ibn ‘Abbas (رضي الله عنه) said: I prayed behind the Messenger of Allah (ﷺ) eight [rak’ahs] together and seven [rak'ahs] together.
Musnad Ahmad 3467Its isnad is saheeh, al-Bukhari (1174) and Muslim (705)]