Guard (The Face of Evil, part 1)

Soon after Neeva delivered the litany, a Sevateem guard came close to capturing the Fourth Doctor and Leela. However, Leela stabbed him with a janis thorn. Though she thought she had behaved appropriately in the circumstance, Leela was swiftly chastised by the Doctor. He wondered who had given her licence to kill and then commanded that she never use janis thorns ever again. (TV: The Face of Evil)