The attack happened just before 1 a.m. near West 135th Street and Malcolm X Boulevard in Harlem.
According to the NYPD, the suspect slashed the 23-year-old man from his ear to his chin on a northbound No. 2 train at the 135th Street subway station before fleeing the scene.
First responders transported the victim to Harlem Hospital, where he is listed in stable condition.
There are currently no arrests as authorities try to determine a motive for the attack.
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