Transit police detectives are looking to find a man who allegedly attempted to assault an MBTA bus driver last Friday after he was asked to wear a face mask while on board the bus in Boston.

According to MBTA transit police, a man boarded an MBTA bus just before 9 p.m. on Feb. 4 at Boston Medical Center, at which point the MBTA bus driver politely asked the customer to wear a face mask.

Transit police say the man ignored the driver's request and continued to talk on his cell phone. The bus driver says that the man was apparently so troubled by his face mask request that he was telling the person on the phone call about it in unpleasant terms.

At some point, transit police say the man approached the bus driver, shouting a profanity and threatening to "stab" him if he didn't "shut up."

Immediately following this threat, the man pulled out a knife and lunged at the bus driver, transit police said. Fortunately the man didn't make any contact with the driver.

Anyone with information on the man's whereabouts or his identity is asked to contact transit police detectives at 617-222-1050, or anonymous texts can be sent to 873873.