Urwah narrates from Sayyidah Aishah (may Allah be pleased with her) that she said: The Messenger of Allah (peace and blessings be upon him) killed only one woman of Banu Qurayzah. By Allah! She was with me, laughing heartily, while the Messenger of Allah (peace and blessings be upon him) was killing their men. Suddenly a caller called out her name: Where is so-and-so? She said: It is I. I said: What is the matter with you? She said: By Allah! I am going to be killed. I asked: Why? She said: Because of something I brought about. She was taken away and beheaded. Sayyidah Aishah (may Allah be pleased with her) said: I have not forgotten this astonishing thing, that she was so cheerful and laughing even though she knew she would be killed. (b) Imam al-Shafi'i (may Allah have mercy on him), in the narration of Abu Abd al-Rahman al-Baghdadi, reports from his associates that she was the woman who had dropped a millstone on Mahmud bin Maslamah (may Allah be pleased with him) and killed him, and she was killed in return for that. It is also possible that she accepted Islam, then apostatized and rejoined her people, and was killed for that reason; and other possibilities exist as well.
Imam al-Shafi'i (may Allah have mercy on him) said: No report is authentic as to why this woman was killed, and it has also been said that Mahmud bin Maslamah (may Allah be pleased with him) was killed at Khaybar; he was not killed on the day of Banu Qurayzah.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب السير / 18107