Musnad Abu Ya'la al-Mawsili 110:280

Narrated to us Shayban, narrated to us Hammam, narrated to us Qatadah, from Ikrimah, from Ibn Abbas regarding the saying of Allah, the Mighty and Majestic: "Mankind was one community" (Al-Baqarah). He said: "They were all upon Islam." And Al-Kalbi said: "It means they were all upon disbelief."