What effect will introducing a kafir’s blood into a Muslim’s body have?

Question

Question: A Muslim fell ill and needed blood. If at that time a kafir’s blood is given, does the sick person’s heart become a kafir’s? Will the children born after the transfusion carry the effect of the kafirs’ blood? After the transfusion, will the Muslim’s habits and manners become like those of the kafirs?

Answer

Using human blood in this way is not permissible; nevertheless, because of it that sick Muslim has not become a kafir, nor has his heart become the heart of a kafir, nor will kufr come upon the children because of it.

Source: Fatawa Mahmudiyya

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