Abu Bakr bin Abd al-Rahman narrates from some of the Companions of the Prophet (peace and blessings be upon him, and may Allah be pleased with them) that one said: I saw that the Messenger of Allah (peace and blessings be upon him), in the year of the Conquest of Makkah, ordered the people on his journey to break their fast, and said: "Gain strength for (facing) your enemy." And the Messenger of Allah (peace and blessings be upon him) fasted. Abu Bakr bin Abd al-Rahman said: The one who narrated the hadith to me said: I saw the Messenger of Allah (peace and blessings be upon him) at al-Arj pouring water over his head because of thirst while he (peace and blessings be upon him) was fasting.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصيام / 8261