A man was slashed by a stranger during an argument at a South Bronx train station Friday night.

The victim — who sources said was in his 30s — got into a dispute with a passenger who then pulled a knife and slashed him on his top lip at the No. 6 train’s Cypress Avenue station shortly after 9:30 p.m., police said.

The victim refused treatment for the minor injury, and the suspect — a middle-aged man — fled the scene, according to the NYPD.

The men did not know each other, and it’s unclear what they were arguing about, cops said