Yazid bin Hurmuz related the story, that Ibn Abbas (may Allah be pleased with them both) wrote to him: You have asked me whether women used to go on military expeditions with the Messenger of Allah (peace and blessings be upon him). Indeed, they used to take part in the expeditions; they would treat the sick and would be given a gratuity from the spoils, but there was no fixed share for them.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب قسم الفيء والغنيمة / 12913