Sahih Bukhari
One-fifth of Booty to the Cause of Allah (Khumus)
Volume: 004 / Book Number: 053 / Hadith Number: 410
Narrated Anas:
The Prophet said, ''Every betrayer will have a flag on the Day of Resurrection" One of the two sub-narrators said that the flag would be fixed, and the other said that it would be shown on the Day of Resurrection, so that the betrayer might be recognized by it.