The term Ahlus Sunnah wal Jamaah can be traced back to the famous companions of the Prophet, Abdullaah ibn Mas’ood and Abdullaah ibn Abbas.The derivation of Ahlus Sunnah can be made from the following verse in Al Imraan, “On the Day (of Resurrection) when some faces will become white and some faces will become black.” (3:106)
Ibn Abbas commented on this verse and said, “followers of the Sunnah and the Jamaah will have faces radiaten with whiteness.”
Ibn Mas’ood commenting on another verse in surah Al Imraan said, “And hold fast, all of you together, to the Rope of Allah, and be not divided among yourselves.” (3:103). He explained that the rope mentioned in the verse was the Jama’ah.
So Ahlus Sunnah wal Jamaah are those Muslims who adhere to the sunnah and who unite upon it, not turning to anything else, whether that be in matters of belief or in matters to do with Islamic rulings (actions). Hence they are called Ahlus Sunnah because they adhere to the Sunnah, and they called al Jamaah because they are united upon following the sunnah.