other than those originally found in them, and the like—then, if he discusses matters unrelated to religion, such as questions of “medicine” and pure “arithmetic” treated in their works, and those who learned from them—such as Muhammad ibn Zakariyyā al-Rāzī, Ibn Sīnā, and other heretical physicians—write material that amounts merely to benefiting from the works of unbelievers and hypocrites in worldly affairs, this is permissible.

This is just as it is permissible to live in their houses, wear their clothes and bear their weapons, or enter into agreements with them to cultivate land, as the Prophet, peace and blessings be upon him, did with the Jews of Khaybar. Likewise, when the Prophet, peace and blessings be upon him, and Abū Bakr left Mecca as emigrants, they hired “Ibn Urayqit”—a man from Banū al-Dīl—as an expert guide, meaning someone skilled in finding the way. They entrusted him with their lives and their mounts, and arranged to meet him at the cave of Thawr on the third morning. Khuzāʿah, both its Muslims and its unbelievers, were trusted confidants and sincere advisers to the Messenger of Allah, peace and blessings be upon him, and he accepted their advice. All this is reported in the two Sahīh collections. Abū Tālib also supported and defended the Prophet, peace and blessings be upon him, despite his polytheism. Such examples are numerous.

Among the polytheists and the People of the Book are trustworthy individuals, as Allah Most High said:

“Among the People of the Book are some who, if you entrust them with a great amount of wealth, will return it to you; and among them are some who, if you entrust them with a single dinar, will not return it to you unless you keep standing over them.”

For this reason, it is permissible to entrust one of them with property, and a Muslim may seek treatment from an unbeliever if he is trustworthy. The leading scholars, including Ahmad and others, expressly stated this, since it involves accepting their accounts of worldly matters within their knowledge and trusting them in those matters. This is permissible provided it does not entail an overriding harm, such as his exercising authority over Muslims, gaining ascendancy over them, or the like. Thus, acquiring medical knowledge from their books is like relying on an unbeliever to find the way or seeking medical treatment from him.