Saying "Alaihis Salam" to the noble Companions?
The words of "Alaihis Salam" and Salat and Salam (blessings and peace) are specific to the Prophets and Angels, peace be upon them; therefore, it is not appropriate to use the words "Alaihis Salam" independently for a non-prophet. However, if other people are mentioned along with the Prophets and they are subordinately included in the greetings as well, then it is permitted. (Kitab-un-Nawazil/Vol: 15/Pg: 97)