Sahih Muslim
The Book Pertaining to the Merits of the Companions (Allah Be Pleased With Them) of the Holy Prophet (May Peace Be Upon Him) (Kitab Al-Fadail Al-Sahabah)
Book Number: 031 / Hadith Number: 6073
'Abd al-Rahman reported that he heard Hassin b. Thabit al-Ansari call Abu Huraira to bear witness by saying: I adjure you by Allah if you had not heard Allah's Apostle (may peace be upon him) saying: Hassin, give a reply on behalf of the Messenger of Allah. O Allah, help him with Ruh-ul-Qudus. Abu Huraira said: Yes, it is so.