Chechnya is mostly Islamic, and Russia was very unfriendly to them, killings tens of thousands of women and children, with the battle of Grozny (twice) being the crowning achievement of civilian deaths.
Syria is mostly Islamic, and Russia has been killing ISIL/ISIS soldiers (and a large number of civilians) there for for about 9 years.
And Afghanistan itself had some slight history with Russia, being at war with them for about a decade.
Yeah in Syria it's one of the few times US and Russian forces have fought "alongside" each other, both against ISIS.** There were so many greenforce nations in Syria the Pentagon had to dedicate staff to coordinate with a crazy mixbag of groups - Syrian Army, FSA, Kurds, Turkish, Russians, Iraq, and even Iran to make sure no one stepped on each other's feet trying to kill ISIS. Lmao they REALLY pissed off the entire planet.
** - Russia quickly started hunting FSA people too and that's how we got the whole "US absolutely deleting Wagner forces at the oil well" incident
Syria: they also allowed Russian Islamic extremists to go fight in Syria rather than cause trouble in Russia - some of them reportedly joined ISIS
Dagestan
Sudan/Darfur
disproportionate recruitment of Muslim minorities for the Ukrainian front
violent repression of Muslim minorities
involvement in the Sahel + helping military regimes in Niger/Mali/Burkino Faso fight ISIS affiliated groups
Afghanistan: ISIS have previously attacked the Russian embassy there, saying the Taliban aren't radicals and are Russian puppets.
Iran: ISIS has perpetrated attacks in Iran, hates the Iranian regime. Iran is a Russian ally and provides them with drones for Ukraine, Russia in turn supports Iran.
the Ukrainian front
violent repression of Muslim minorities
An important distinction. There are a lot of ethnic minorities in Russia, and a lot of them are Muslim. The biggest groups got their own "stan" and are nominally independent now, but plenty in country.
One of the reasons Chechnya got hammered so hard in the 90s was to send a message to those groups. But they ain't happy.