1 Question: If an organ of an atheist is transplanted in a Muslim’s body, would it be considered ritually pure (Tãhir) when it is considered, after transplantation, as part of the Muslim’s body?
Answer: An organ or limb extracted from the body is ritually impure (najis) irrespective of whether it came from a Muslim or a non-Muslim. And when it becomes, by rejuvenation, part of a Muslim’s body or of someone who is considered a Muslim, it becomes Tãhir.sistani.org/14916
2 Question: Is mercy killing allowed?
Answer: No, mercy killing is not permissible.sistani.org/25300
3 Question: Is it permissible to remove a life-support machine attached to a dying person, and the doctors state there is no hope in his recovery, with certainty that he will die shortly later?
Answer: It is not permissible at all to remove it.sistani.org/25302