Allah SWT said in Surat Al Nisa Ayat No. 86 & 87.
86. And when you are honoured with (a word of) greeting, then (in reply) greet with a better (salutation) or (at least) reciprocate (in the same words). Surely Allah takes an account of everything.
87. Allah is He apart from Whom there is none worthy of worship. He shall certainly gather you on the Day of Resurrection about which there is no doubt. And who is more truthful in word than Allah?
Purpose of this thread is when u hear/read u should reply/wrote 
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