Yazid bin Hurmuz (may Allah have mercy on him) said that Najdah wrote to Abdullah bin Abbas (may Allah be pleased with them both), asking him about certain matters. Abdullah bin Abbas (may Allah be pleased with them both) said: People say that Ibn Abbas corresponds with the Haruriyyah, and were it not that I fear concealing knowledge, I would never write to him. Najdah wrote to him: "Amma ba'd (To proceed)": Tell me, did the Messenger of Allah (peace and blessings be upon him) take women with him on military campaigns, and did he (peace and blessings be upon him) assign them a share? Did he (peace and blessings be upon him) kill children? When does the orphanhood of an orphan come to an end? And tell me about the khumus (one-fifth): for whom is it? Then Abdullah bin Abbas (may Allah be pleased with them both) wrote to him: You have asked me whether the Messenger of Allah (peace and blessings be upon him) took women with him on campaigns. He said: Yes, women did take part in campaigns with him (peace and blessings be upon him), but they would dress the wounds of the injured and nurse the sick, and they would be given something from the spoils, but they had no fixed share. And he (peace and blessings be upon him) did not kill children, so you too must not kill them, unless you come to know about those children what Khidr (peace be upon him) knew, and likewise distinguish between the believer and the disbeliever, so that you kill the disbeliever and leave the believer. You have also written asking when the orphanhood of an orphan is complete and finished. Abdullah bin Abbas (may Allah be pleased with them both) said: By my life! Sometimes a man's beard grows and he has no understanding of dealings; he is completely weak in this matter. Whoever attains the understanding that other people have, his orphanhood comes to an end. And you have asked me about the khumus: we used to say, it is for us, but our people refused us that (saying it is not yours), so we bore it patiently.
And in another narration: As for slaves and women, there was no fixed share for them when they were present in battle, but they would take something from the people's spoils.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب السير / 17811