The Book of Jihad and Expedition (Kitab Al-Jihad wa'l-Siyar)
Muslim :: Book 19 : Hadith 4454
It has been narrated on the authority of Anas b. Malik who said that the Messenger of Allah (may peace be upon him) allowed Umm Sulaim and some other women of the Ansar to accompany him when he went to war; they would give water (to the soldiers) and would treat the wounded.
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