Sahih Muslim | Book 38 | Hadith Number 6689

Narrated by Qais b. 'Ubad
Qais b. 'Ubad reported: We said to 'Ammar: Was your fighting (on the side of 'Ali in the Battle of Siffin) a matter of your own choice or you got its hints from Allah's Messenger (may peace be upon him) for it, is likely for one to err in one's own discretion or was it because of any covenant that Allah's Messenger (may peace be upon him) got from you? He said: It was not because of any covenant that Allah's Messenger (may peace be upon him) got from us which he did get from other people, and he further said that Allah's Messenger (may peace be upon him) said: "In my Ummah." And I think that Hudhaifa reported to me and according to Ghundar (the words are) that he said: In my Ummah, there would be twelve hypocrites and they would not be admitted to Paradise and they would not smell its odour, until the camel would pass through a needle's hole. Dubaila (ulcer) would be enough to (torment them)-a kind of flame of Fire which would appear in their shoulders and it would protrude from their chest.