Well, what time you mean? There was never some organized muslim invasion. Just first migration from Arabian Peninsula and after that expansion of many muslim states, which was normal part of geopolitical game - they were warring with christian states as with other religions, islamic states included.

Ummayad Expansion into Iberian Peninsula and western France was stopped by logistics. After conquering footholds and bigger part of Peninsula, political situation and supply lines meant Franks were under attsck raiding parties, not organized military invasion. Closest thing to resemble crucial battle is Battle of Tours, but our sources are scant. Historians cant even agree on number of soldiers. But, this part of campaign was closest to resembling conquering spearhead. In final it proved more important for Franks than Ummayads, because it made them one of regional powers. Instability in Egypt, Syropalestine and Maghreb caused more inward focus for Ummayads and successor states.

Seljuks were stopped by pressure from Mongols in the east.

Or you can jump to Ottoman Empire, but that was really, really long process. Ottomans were part of medieval and modern clashes. You can say their part in Europe was ended with dissolution of Caliphate and Ataturk's reforms. But we are talking about long regress from Ottoman hearthland and inability to cope with rapid industrialization of european powers and huuuge decentralized empire which began to fall apart and was threatened by Russian aggresion.

Short answer is, there is no defining battle for we must make distinction between different states which were subjects to a number of influences, external and internal. Andalusia, Ummayad, Abbasid, Fatimids, Almoravids, Seljuks, Ottomans...