Source: silsilat ul-hudaa wa nnoor – the series of guidance and light – tape no. 253
Question #2: “What is the authenticity of adding wa maghfiratuh in offering thesalaam and responding to it?”
Shaykh al-Albaani (rahimahullaah) answers:
“There is no addition (of wa maghfiratuh) in the hadeeth with respect to offering the salaam; i.e., if a person starts with offering the salaam, he ends at wa barakaatuh: asalaamu ‘alaykum wa rahmatullaahi wa barakaatuh. And thehadeeth that has come – or in more precise words, (the hadeeth) that was narrated – (stating) that at the fourth time, the fourth of them said, asalaamu ‘alaykum wa rahmatullaahi wa barakaatuh wa maghfiratuh, then this is a weak narration. As for the addition (of wa maghfiratuh) in the response to wa barakaatuh, then it is established; i.e., a man says, asalaamu ‘alaykum wa rahmatullaahi wa barakaatuh, then we add wa maghfiratuh in the response…
It is in agreement with the noble Qur’aan (with) the saying ‘When you are greeted with a greeting, greet in return with what is better than it, or (at least) return it equally.’ So if the greeter gives the salaam, saying asalaamu ‘alaykum wa rahmatullaahi wa barakaatuh, the aayah that stated ‘greet in return with what is better than it’ is not invalidated; this command still exists, which is (followed by saying) wa maghfiratuh. This addition (with respect to responding) has also been mentioned in…narrations established from some of the Companions.
So we have brought out a conclusion whose summary is that adding wa maghfiratuh in the response is allowed and starting (the salaam with it) is not allowed.”
 saying ‘and His Forgiveness’ after the greeting ‘may Peace, Mercy and Blessings of Allaah be upon you’
 Surat un-Nisaa, 4:86