Organ transplantation is a very lengthy issue, and we have discussed it more than once, but in general, if there is no harm.
For example, the donor gives a kidney and can live with the other kidney.
InshaAllah. I say, if this person who donates this kidney can live his life normally.
And it does not harm him in any way, and with the testimony of a doctor, then he may donate it to someone else, and there is no problem.
As for selling, it is not allowed. As for the issue of organs other than the kidney, organs that a person donates after his death.
There is a long-standing difference of opinion among the scholars about this, because some scholars believe that a person does not own his organs to donate them.
The human body is not owned; if he cuts off his hand, he will be held accountable for this, as we just mentioned a little while ago.
He commits a sin or wrongdoing, or whoever does evil or wrongs himself. All of this means that a person does not own these organs; they are not his property.
So that he can give them to someone else as a gift or otherwise, let alone his heirs.
For example, his heirs inherit his wealth, but they do not inherit his organs.
So that they can donate them. But if this organ does not affect his life,
then it is permissible for him to donate it. But if it affects his life or he donates it after his death, then this is a matter of consideration.
In reality, there is a lengthy discussion among the scholars, and the closest opinion is that this is never valid.