مُسْنَدُ أَحْمَدَ
Musnad Ahmad 2453
Musnad of 'Abdullah bin al-'Abbas bin 'Abdul-Muttalib from the Prophet
'Amr bin Deenar said: I heard Jabir bin Zaid say: I heard Ibn 'Abbas (رضي الله عنه) say: The Messenger of Allah (ﷺ) prayed eight [rak'ahs] together [i.e., he put Zuhr and ‘Asr together] and seven [rak'ah's] together [i.e., he put Maghrib and 'Isha' together].
Musnad Ahmad 2465Its isnad is saheeh, al-Bukhari (562) and Muslim (705)]