Musnad Ahmad 1118:14

Yahya ibn Ishaq narrated to us, he said: Ibn Lahi'ah informed us, from Yazid ibn Abi Habib, from Abu Marzuq, from Hanash, from Fadalah ibn 'Ubayd: That the Messenger of Allah (peace and blessings of Allah be upon him) began his day fasting, then he called for a drink. Some of his companions said to him: "O Messenger of Allah, did you not begin your day fasting?" He said: "Yes, but I vomited."