I must say good night
A phrase that precedes one's departure at nighttime. Adam's waiting for me at home, so I must say good night. Ooh, the last train comes in five minutes, so I must say good night, my friends!
I must say good night.
an expression announcing the speaker's intention of leaving for the night. Jane: It's late. I must say good night. Bob: Can I see you again? Jane: Call me. Good night, Bob. Bob: Good night, Jane. Sue: I must say good night. Mary: Good night, then. See you tomorrow.