the original text itself. What is regrettable is that these marginal notes contain no benefit and may even be erroneous. This is unlawful and impermissible. A borrower may never write even a single letter in a borrowed book. Even if he finds an error, he has no right to correct it unless he obtains the owner’s permission, for he may think that a phrase is mistaken when it is actually correct.

What, then, may be lent for use? He said: “It is permissible to lend for use anything that has a lawful benefit.” Thus, any tangible item that has a lawful benefit may be lent for use. This excludes things that have no benefit, such as worms, cockroaches, dung beetles, beetles, and the like. It is not permissible to lend these, because they have no intended benefit.

The benefit must also be lawful. If an item has an unlawful benefit, it may not be lent for use, such as drums, musical instruments, and the like. Lending them is unlawful because their benefit is unlawful. This also includes lending a female singer so that she may sing unlawfully; lending her for this purpose is unlawful. The evidence is Allah’s saying: “And do not cooperate in sin and transgression” [al-Mā’idah 5:2]. Lending something whose benefit is unlawful is undoubtedly cooperation in that unlawful benefit.

Thus, if someone wished to lend another person a vicious dog, saying, “People frequently come near my farm; lend me your vicious dog so that it may attack everyone who passes around it,” this would not be permissible. A vicious dog may not even be kept as one’s property; rather, it must be killed. Indeed, the Messenger of Allah ﷺ permitted its killing both within and outside the Sacred Precinct, as stated in the authentic hadith: “Five kinds of creatures