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Shaykh Faraz Rabbani from SeekersHub addresses this question in the video below:
Properly, one should say Asalaamu alaykum warahmatullah, right? The sunnah is fulfilled by saying Asalaamu alaykum warahmatullah. In the Hanafi school, that is the sunnah.
And the minimum thing to say is Asalam. But properly the sunnah is to say Asalaamu alaykum warahmatullah.
Many people are lazy about it and they say Asalaamu alaykum warahmatullah [mumbled]. When you hear another person, it’s easy to mumble certain letters. So, say Asalaamu alaykum warahmatullah, it’s hard to say was that Asalamu Alaikum or Salamu Alaikum.
All right, sometimes it’s in between. So, you give others the benefit of doubt. In the Hanafi school, that does not affect the validity of the prayer. The wajib is fulfilled.
If you say Salam, basic wajib is fulfilled. But properly you say Asalaamu alaykum warahmatullah for the sunnah. And the Shafi school is very strict about this as well. But there’s some leeway regarding that even in that school.
I hope this helps answer your question. You can also check out more from SeekersHub at the link here.
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