مُسْنَدُ أَحْمَدَ
Musnad Ahmad 3843
Musnad of Abdullah bin Mas'ood
It was narrated that ‘Abdullah (رضي الله عنه) said: The Messenger of Allah (ﷺ) said: "I will reach the Cistern ahead of you, and I will plead for some people of my ummah, but I will have to give them up. I will say: O Lord, my companions. But it will be said: You do not know what they did after you were gone."
Musnad Ahmad 3866Saheeh and its isnad is hasan, al-Bukhari (6576) and Muslim