In his book Mu’jam Al Minaahi Al-Lafdhiyyah (Glossary of Forbidden Words), Sheikh Bakr Abu Zaid wrote in reply to one of the magazines where a person said:
“Most of the people when they meet each other, they greet by saying, “Sabah al-khair….” Or, “Masaa al-khair.” And the reply to this greeting is by saying, “Sabah an-noor.” Or “Masaa an-noor.””
This greeting is the greeting of the Magians. The Magians believe in two powers: The power of good and the power of evil which are represented by noor and dhalamah (darkness).
So, the Magians have a god for khair or noor as well as a god for evil or dhalamah (darkness) and they are fighting amongst each other to control this world. That is why they deemed it reasonable to greet one another by saying, “Sabah al-khair” and “Sabah an-noor.”
Whereas in Islaam, we have been instructed to greet each other wit the greeting of peace: “Assalaamu alaikum.” Which replaces all other types of greetings. So it is not benefiting for the Muslims to substitute this greeting by saying, “Sabah al-khair.” Or “Sabah an-noor.”
Abu Imad Rasheed Gant – CalgaryIslam.com