إذَا سَلَّمَ عَلَيْكُمْ أَهْلُ الْكِتَابِ فَقُولُوا: وَعَلَيْكُمْ

Transliteration:

If one of the People of the Scripture (i.e. Christians and Jews) greets you, saying As-Salāmu `alaykum, then say (to him):

Translation:

If one of the People of the Scripture (i.e. Christians and Jews) greets you saying As-Salaamu `alaykum, then say (to him): And upon you .