Wa `alaykum as-salamu wa rahmatullahi wa barakatuh.
In the Name of Allah, Most Gracious, Most Merciful.
All praise and thanks are due to Allah, and peace and blessings be upon His Messenger.
Dear questioner, thanks a lot for your question which reflects your care to have a clear view of the teachings of Islam. Allah commands Muslims to refer to people of knowledge to get themselves well-acquainted with the teachings of Islam as well as all aspects of life.
Regarding your question, it should be clear that Islam carries for humanity all goodness and welfare. Muslims are commanded to keep good relations with and be generous to all peoples. Therefore, a Muslim is allowed to donate blood to a non-Muslim.
In his response to the question, Dr. Muzammil Siddiqi, President of the Islamic Society of North America, states,
Blood transfusion for medical purposes is permissible in Islam. It is permissible to take blood from a non-Muslim and it is permissible to give blood to non-Muslims. These matters are related to human life.
It stands to reason that Islam teaches us to feed the hungry, to take care of the sick and to save the life of people. In these matters, it does not make any difference between the life of a Muslim and non-Muslim.
Allah Almighty knows best.