Is buying a kidney or any other human organ forbidden (haram) if it is the only solution to save a patient's life and there is no donor from their family who meets the medical requirements?

If a person needs a kidney to preserve their life, it is permissible for them to donate it. If they do not find a donor but find someone who sells their kidney, it is permissible for the patient to buy it out of necessity. In this case, the sin rests upon the seller of the kidney. The patient's relatives are not obligated to donate to them.