A mumbling maniac stabbed a man in an unprovoked Brooklyn attack Tuesday night, police said. 

The 32-year-old victim was walking on Seventh Avenue near Lincoln Place in Park Slope just after 9 p.m. when the complete stranger muttered something as he approached, cops said.

Then the menace suddenly knifed the pedestrian in the chest, cops said. 

The injured man was taken to Brooklyn Methodist Hospital, where he is listed in stable condition, authorities said. 

The attacker fled on foot and hadn’t been caught Wednesday. 

He was last seen wearing a white shirt, gray sweatpants and black pants, cops said. 

A knife was recovered, according to police.