The stabbing happened at the Broadway Junction A/C Station between Fulton Street and Van Sinderen Avenue in East New York.
Police said the victim, who had been selling newspapers on the A train, was stabbed in the back after a confrontation.
The suspect, who fled the scene, is described as a black male in his 20s, approximately 6 feet tall, wearing a black shirt, black pants and a purple hat with an orange line.
The victim is in stable condition at Brookdale Hospital Medical Center.
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