Greeting in Islam is one of the teachings in Quran and authentic Hadeeths. Those who submit to the Will of Allah and believe fully in Islam, use the greeting which has been mentioned in Quran and Hadeeth. Those who use other greetings are been blamed in Quran (And when they come to you,v they greet you with a greeting which Allah never greeted you with) Sura 58, Verse 8.

Allah Says in Quran : (When you enter the house, then greet one another with the greeting from Allah, blessed and nice.) Sura 24, verse 61.

'Muslim should greet Muslims with the greeting of Allah which is Salam and never use the greetings of non Muslims when greetings Muslims.

It is narrated that a person greeted the Prophet Muhammad (SAWA) by saying : Good morning عِمتَ صباحا. The Prophet replied him: Allah Has replaced it with better greeting; Salaam.

'Wassalam.