مُسْنَدُ أَحْمَدَ
Musnad Ahmad 4321
Musnad of Abdullah bin Mas'ood
It was narrated that 'Abdullah bin Mas'ood (رضي الله عنه) said: The Messenger of Allah (ﷺ) said: “I will reach the Cistern ahead of you, and some men will be snatched away from me. I will say: 'O Lord, my companions!’ It will be said: ‘You do not know what they did after you were gone.’”
Musnad Ahmad 4351Saheeh; its isnad is qawi]