Musnad Ahmad 25:505

Ya'qub narrated to us, he said: My father narrated to us, from Ibn Ishaq, Bashir ibn Yasar, the freed slave of Banu Harithah, narrated to us, from Abdullah ibn Abbas, who said: "The Messenger of Allah, may Allah bless him and grant him peace, went out in the year of the Conquest during Ramadan. He fasted Ramadan, and the Muslims fasted with him, until when he was at al-Kadid, he called for water in a wooden bowl while he was upon his riding beast. He drank while the people were looking, teaching them that he had broken his fast, so the Muslims broke their fast."