expression
three days and three nights
Fixed expression used to emphasize a continuous duration of three full days and nights, often in contexts of effort, travel, or endurance.
三日三晩、ほとんど寝ずに働いた。
I worked almost without sleep for three days and three nights.
三日三晩の雨で川が氾濫した。
The river flooded after three days and three nights of rain.