مُسْنَدُ أَحْمَدَ
Musnad Ahmad 3761
Musnad of Abdullah bin Mas'ood
It was narrated that ‘Abdullah (رضي الله عنه) said: The Messenger of Allah (ﷺ) said: "Islam began as something strange and will go back to being something strange as it began, so glad tidings to the strangers.” It was said: Who are the strangers? He said: “Those who are alienated from their tribes.”
Musnad Ahmad 3784lts isnad is saheeh]