If a non-Muslim says As-Sam ‘alaykum, you should respond by saying Wa ‘alaykum. If a non-Muslim greets you saying As-salamu ‘alaykum, the majority of scholars said that we have to return the greeting, and this is the correct view.

The Prophet (peace and blessings be upon him) made spreading salam a part of faith. Salam sows seeds of love and friendship in the hearts of Muslims. The Prophet (peace and blessings be upon him) commanded us to return salam and made it a right and a duty.