Musnad Ahmad 25:1399

Muhammad ibn Bakr narrated to us, Ibn Jurayj informed us, he said: Ibn Shihab informed me, from Ubayd Allah ibn Abd Allah ibn Utbah, from Ibn Abbas, from the Messenger of Allah (may Allah bless him and grant him peace): "That he went out in the year of the Conquest in the month of Ramadan, and he fasted until he reached al-Kadid, then he broke his fast."