If one of the People of the Scripture (i.e. Christians and Jews) greets you, saying:

As-Salāmu `alaykum,

then say (to him):

Wa `alaykum.
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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 .