It is also needed in transactions undertaken on behalf of others: those conducted by someone entrusted with the affairs of Muslims, an orphan, an endowment, or others; those conducted by an agent, such as an agent authorized to transact, a business partner, or the managing partner in a profit-sharing venture; and those conducted by someone whose property is subject to another person’s rights, such as a sick person.

It is also needed for purchases required in fulfilment of duties to Allah Most High—such as water for purification, clothing to cover oneself in prayer, and equipment for Hajj—or duties owed to other people, as in obligatory transactions, such as … Its basis is analogy and comparing a thing with its like.

It is justice itself, and the very conduct recognized as right that is encompassed by His words:

“He enjoins upon them what is right,”

and His words:

“Enjoin what is right.”

This is agreed upon among Muslims—indeed, among all the people of the earth—for it involves comparison between particular instances to which rulings apply, rather than between categories of rulings. It is part of the equity for which Allah sent the messengers and revealed the scriptures. It means repaying good with its like, and evil with its like, as Allah Most High says:

“Is the reward for good anything but good?”

And He says:

“When you are greeted with a greeting, respond with a better greeting or return it in kind.”

And He says:

“The recompense for an evil deed is an evil deed like it.”

And He says:

“Prescribed for you is retribution in cases of killing.”

And He says:

“So whoever attacks you, retaliate against him in the same measure as his attack upon you.”

And He says:

“If you retaliate, then retaliate to the same extent as the injury inflicted upon you.”

However, repaying good with its like is obligatory justice, while giving more is a recommended act of kindness