Imam Malik's Muwatta, Chapter: Fasting

Yahya related to me from Malik from Sumayy, the mawla of Abu Bakr ibn Abd ar-Rahman, from Abu Bakr ibn Abd ar-Rahman from one of the companions of the Messenger of Allah, that the Messenger of Allah, may Allah bless him and grant him peace, ordered everyone to break the fast on the journey he made in the year of the conquest saying, "Be strong for your enemy," while the Messenger of Allah, may Allah bless him and grant him peace, kept on fasting. Abu Bakr said that the one who related this to him said, "I saw the Messenger of Allah, may Allah bless him and grant him peace, pouring water over his head at al-Arj, either from thirst or from the heat. Then some one said to the Messenger of Allah, may Allah bless him and grant him peace, 'Messenger of Allah, a group of people kept on fasting when you did.' Then when the Messenger of Allah was at al-Kadid, he asked for a drinking-bowl and drank, and everyone broke the fast."