مُسْنَدُ أَحْمَدَ
Musnad Ahmad 4173
Musnad of Abdullah bin Mas'ood
It was narrated from ‘Abdullah from The Prophet (ﷺ) that He said: "Every betrayer will have a banner on the Day of Resurrection.” Ibn Ja'far said: "And it will be said: This is the betrayer of So and so."
Musnad Ahmad 4201Its isnad is saheeh, al-Bukhari (3186) and Muslim (1736)]