Musnad Abu Ya'la al-Mawsili 155:177

Ibrahim ibn Sa'id narrated to us, Abu al-Yaman narrated to us, Shu'ayb informed us, from al-Zuhri: Abu Salamah ibn 'Abd al-Rahman informed me that he heard Hassan ibn Thabit al-Ansari asking Abu Hurayrah to bear witness, saying: "I adjure you by Allah, did you hear the Prophet, may Allah bless him and grant him peace, say: 'O Hassan, answer on behalf of the Messenger of Allah. O Allah, support him with the Holy Spirit'?" Abu Hurayrah said: "Yes."