Ontario police said Monday they arrested a man caught on cell phone video attacking a driver with a knife.

The witness who recorded the violent incident told NBCLA it happened at the intersection of Mountain Boulevard and Holt Avenue on Saturday afternoon when a white vehicle cut off another driver.

The witness, who asked to remain anonymous for fear of retaliation, said he was behind the two vehicles at the time of the incident.

The video shows the moment the driver of the white car, accompanied by a woman, pulls out a knife and repeatedly stabs the driver in the arm.

The witness said the drivers of the two vehicles were yelling at each other through open windows, and at one point, the woman threw water or some type of liquid at the other vehicle.

The person who shot the video told NBCLA he was with his family and left the scene fearing the incident would escalate.

The Ontario Police Department confirmed to NBCLA they arrested the man with the knife thanks to the cell phone video and other surveillance video provided.