Musnad Ahmad 25:521

Ya'qub narrated to us, my father narrated to us, from Muhammad ibn Ishaq, Al-Hajjaj ibn Artah narrated to me, from 'Ata' ibn Abi Rabah, he said: I heard Ibn Abbas saying: "The Messenger of Allah, peace and blessings of Allah be upon him, passed away while I was uncircumcised."