How to reply to a disbeliever if he says Salam to you
If one of the People of the Scripture (i.e. Christians and Jews) greets you saying As-salaamu ‘alaykum, then say (to him) وَعَلَيْكُمْ Wa ‘alaykum And upon you Al-Bukhari, cf. Al-Asqalani, Fathul-Bari