Praise be to Allah.
It is permissible for a Muslim to donate blood to a non-Muslim, except when that non-Muslim
is known to be in a position of fighting the Muslims (either by belonging to a state which is in a
state of war with Muslims or by supporting aggression towards them). In such a case it is not
permissible to donate blood, because this will help them to fight Muslims. If the Muslim has no
way of knowing to whom his blood will go, he should act according to what he thinks is most
likely to happen. If he thinks that it is most likely to go to a kaafir who is not fighting the
Muslims, it is permitted to donate, otherwise it is not.