Good Manners and Form (Al-Adab)
Bukhari :: Book 8 :: Volume 73 :: Hadith 173
Narrated Abu Salama bin 'Abdur-Rahman bin 'Auf:
that he heard Hassan bin Thabit Al-Ansari asking the witness of Abu Huraira, saying, "O Abu- Huraira! I beseech you by Allah (to tell me). Did you hear Allah's Apostle saying' 'O Hassan ! Reply on behalf of Allah's Apostle. O Allah ! Support him (Hassan) with the Holy Spirit (Gabriel).'?" Abu Huraira said, "Yes."