مُسْنَدُ أَحْمَدَ
Musnad Ahmad 3743
Musnad of Abdullah bin Mas'ood
It was narrated that ‘Abdullah (رضي الله عنه) said: I prayed with The Messenger of Allah (ﷺ), and he stood for such a long time that I thought of doing something bad. We said: What was it? He said: I thought of sitting down.
Musnad Ahmad 3766Its isnad is saheeh, al-Bukhari (1135) and Muslim (773)]