Musnad Ahmad 1018:100

Sulayman ibn Harb narrated to us, Hammad ibn Salamah narrated to us, from Ali ibn Zayd, from al-Hasan, from al-Ahnaf, who said: While I was circumambulating the House (the Kaaba), a man from Banu Sulaym met me and said: "Shall I not give you glad tidings?" I said: "Yes." He said: "Do you remember when the Messenger of Allah (peace and blessings of Allah be upon him) sent me to your people, the Banu Sa'd, to invite them to Islam?" I said: "By Allah, you have said nothing but good, and I hear nothing but good. For I returned and informed the Prophet (peace and blessings of Allah be upon him) of your statement, and he said: 'O Allah, forgive al-Ahnaf.'" He said: "There is nothing I am more hopeful for than that (supplication)."