Musnad Ahmad 1118:2

Muhammad ibn Ubayd narrated to us, Muhammad ibn Ishaq narrated to us, from Yazid ibn Abi Habib, from Abu Marzuq, from Fadalah al-Ansari, I heard him narrating: That the Messenger of Allah, peace and blessings of Allah be upon him, went out to them on a day he was fasting. He called for a vessel containing water and drank. We said: "O Messenger of Allah, you used to fast this day." He said: "Yes, but I vomited."