Someone stated:

"Naturally, the expression "Ahl al-Sunnah" was unknown in the early days of Islam."

The expression "Ahl al-Sunna" is reported from Ibn `Abbas and Ibn `Umar by al-Lalika'i in Sharh Usul I`tiqad Ahl al-Sunna; Muslim narrates it from Muhammad ibn Sirin in the Muqaddima to his Sahih; and al-Darimi in his Musnad from al-Hasan al-Basri. This is not to mention the Mujtahid Imams and those of the generation-layer immediately preceding them.

I could look up al-Suyuti's compilation Miftah al-Janna fi al-Ihtijaj bis- Sunna and the late Dr. `Abd al-Khaliq Abd al-Ghani's Hujjiyyat al-Sunna for more reports, but this is probably enough to put to rest the false assumption that the expression was unknown in the early days of Islam.