It happened on an express service minibus in Clifton on Monday.
Surveillance video shows the victim being beaten and then stabbed by two other passengers after an argument over a seat.
It happened so fast, other passengers barely had a chance to jump in and help.
Police say if the bus hadn't been so close to a hospital the man who was stabbed may have died.
The man and woman who attacked the victim have not been found.
They escaped on another bus after the stabbing.
Police are hoping the surveillance video will lead to an arrest.
The victim remains hospitalized.