It was on 11 June 806 that the Abbasid caliph Harun al-Rashid took a very large army assembled at Raqqa, in what is now Syria, and raided the Asia Minor holdings of the Byzantine emperor Nikephoros in Cappadocia.
The sacking of the city of Herakleia became a popular point of pride in the Arab world for centuries to come, all the way to the Ottomans, not least because a monument to the victory that was apparently many times more lavish than most of the Roman triumphal arches that we may be familiar with was built just outside Raqqa and called Hiraqla - the ruins of it are still there today, if you get the chance during a tour of Syria.
The invasion didn't change much at the time, though, because like other dynasties and caliphs the Abbasids tended to go on raids and then just turn around and leave with whatever plunder was convenient. The Byzantines on the losing side broke the terms of their surrender treaty almost immediately, as well.
https://en.wikipedia.org/wiki/Abbasid_invasion_of_Asia_Minor_(806)