Police said the stabbing happened at the 47th Street station in Fuller Park just before 3 p.m.
A 35-year-old man was arguing with someone when that person took out a "cutting instrument" and swung at him, police said.
Police said the victim, cut in the face and hand, was transported to the University of Chicago Medical Center in good condition.
There is no one in custody, and Area One detectives are investigating.
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