Sahih Bukhari Volume 4, Book 52, Hadith Number 131.

Narated By Anas : On the day (of the battle) of Uhad when (some) people retreated and left the Prophet, I saw ‘Aisha bint Abu Bakr and Um Sulaim, with their robes tucked up so that the bangles around their ankles were visible hurrying with their water skins (in another narration it is said, “carrying the water skins on their backs”). Then they would pour the water in the mouths of the people, and return to fill the water skins again and came back again to pour water in the mouths of the people.