Is it permissible to kill those who fight among the specified categories (including women, the elderly, and monks)?

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It is permissible to kill anyone who fights from the specified groups, including women, the elderly, and monks engaged in battle. This ruling is unanimously held by the scholars, including Al-Awza'i, Al-Thawri, Al-Layth, Al-Shafi'i, Abu Thawr, and the Ahl al-Ra'i. The evidence includes the Prophet's action of killing a woman on the day of Qurayza who was casting a millstone upon Mahmud ibn Maslama. Furthermore, the Prophet (peace be upon him) upon passing a slain woman on the day of the Trench asked, "Who killed this?" and when the killer replied it was because she was disputing with him regarding his sword's scabbard, the Prophet remained silent, indicating that the prohibition against killing a woman only applies if she is not fighting.