What is the ruling on donating kidneys or buying them?

The questioner : Regarding the topic of kidneys, we have now taken up the evidence of those who prohibit kidney donation, and this is clear, because kidney donation currently exists, and there is no doubt that they relied on something.

The Shaykh : Yes, and then they relied on the Mushaf.

The questioner : The same, I mean.

The Shaykh : Their evidence is only maslahah (public benefit); they have absolutely no evidence from the Book or the Sunnah for the existence of such a thing, except that they said this is a benefit and that there is no harm in it. So we say: even if we concede that for a deceased person there is no harm except for the mutilation, we do not concede it for a living person. The benefit from the organs of the body is sufficient. In any case, this is a second issue. I mean, if a person is afflicted with kidney failure, and he knows and finds a kidney that is sold, not one that is taken for that purpose, but one that is sold and ready, is it permissible for him to buy from it? We say it is permissible for him to buy from it, because its harm has already materialized before he came, and if it is more likely than not that it will benefit him, he buys from it, and there is no obstacle.
And the like of that is the heart. They say now there are hearts hanging, sold, human hearts. If one of the people is afflicted with a heart disease, he buys from them. Yes, but they are not hanging, salted, or sliced like meat, but preserved with things. Yes. So is it permissible for a person to buy the heart of a disbeliever? Yes.
This is a problem. It is true that it has confused some people. One asks and says: Is it permissible for me to buy the heart of a disbeliever? And the Messenger (peace and blessings be upon him) says: If the heart is sound, . And if I were to install a disbeliever's heart tomorrow, it would order me to commit kufr (disbelief) because it is a heart that is not sound. So what is the answer?
We say this is not applicable. Because thinking in reality and all conceptions are in the brain. The heart is nothing but an administrator. It administers what comes to it.
So the brain is the secretary. It beautifies and prepares everything, then sends it to the heart for signing and execution, and this is an abstract matter. For this reason, when a problem comes to a person, you find him saying, I mean, thinking. He does not say it this way; he puts his hand on his head to think. And after he thinks, the brain takes the order from the heart. This is the best way to reconcile the hadith with reality: to say that thinking is undoubtedly in the brain, and this is something in which a person does not prevent it. So when the matter is completed, it is sent to the king to take the orders and the signature. And on this basis, if the heart of a disbeliever is placed in the body of a Muslim, it will rule over things according to what comes to it from the brain.