The image below  is a screen shot  displaying Reliance of the Traveller, Book O, Ch. 9.13 as it appeared in my browser, which was pointed to  the search result from http://www.muhaddith.org/cgi-bin/e_optns.exe.  Muhaddith is an Islamic web site which maintains a large library consisting mostly of Arabic texts. Reliance of the Traveller is one of the few English translations  available there.  Maktabh.org has a Scribid version of Reliance that will be easier to search and read than the text version which serves as my source.

    Islam's prohibition of killing women and children in warfare is claimed by Muslims and their apologists as a badge of Islamic moral superiority.  In reality, it is far from a badge of morality; it is bright shining sign of Islam's mercenary mission.  

    The prohibition is not based on morality, it is based on economics.  Dead women and children have no value on the slave market.  Captured women and children become slaves by reason of capture.  

    In case some scintilla of doubt remains, I present the clincher: a clear statement on the subject from an eminent Islamic Jurist.I have added emphasis to the critical clause in the last sentence of the quote.

Since lawful warfare is essentially jihad and since its aim is that the religion is Allah’s entirely [2:189, 8:39] and Allah’s word is uppermost [9:40], therefore, according to all Muslims, those who stand in the way of this aim must be fought.

As for those who cannot offer resistance or cannot fight, such as women, children, monks, old people, the blind, handicapped and their likes, they shall not be killed, unless they actually fight with words [e.g. by propaganda] and acts [e.g. by spying or otherwise assisting in the warfare].

Some [jurists] are of the opinion that all of them may be killed, on the mere ground that they are unbelievers, but they make an exception for women and children since they constitute property for Muslims.

The source of that quote is The Religious and Moral Doctrine On Jihad  by Ibn Taimiyyah.
http://www.crusadersarmory.co.cc/Enslavement of Captives.jpg