What is the ruling on buying or renting something intended for use in both lawful and unlawful matters, and does the ruling differ if the predominant use is lawful or unlawful? And is it forbidden to use the thing itself in lawful matters if its purchase was unlawful?

Al-Shatibi said: "The Legislator intends for the accountable person's intention in action to align with His intention in legislation." Therefore, it is impermissible to purchase or rent something with the intention of using it for unlawful purposes, even if it is not inherently unlawful. Examples include selling wood to someone who will use it as a cross, grapes to someone who will press them into wine, or weapons to someone who will use them for banditry or to incite discord.

It is stated in the Fatawa of Ibn Hajar al-Haytami that it is forbidden to sell musk to a disbeliever who will use it for his idol, and to sell an animal to a belligerent non-Muslim who will kill it without proper slaughter. This is because anything which the seller knows the buyer will use for disobedience is forbidden for him to sell, as disbelievers, like Muslims, are addressed by the subsidiary rulings of the Sharia. Thus, assisting in disobedience is not permissible, and here, dominant conjecture is considered equivalent to certain knowledge.

Accordingly, purchasing or renting something permissible with the intention of using it for unlawful purposes is impermissible for the buyer or renter due to their intention. If the seller or lessor is aware of this, it is forbidden for them to engage in the transaction. The ruling is based on what is generally prevalent, not what is rare.

As for the ruling on the permissible use of something purchased or rented for an unlawful purpose, there is no harm in using it for what is permissible, but its use for what is unlawful is forbidden.