寝言は寝て言え
Meanings
1
don't talk nonsense; stop talking rubbish
jocular, humorous
A humorous, idiomatic retort meaning 'That's nonsense; you're talking in your sleep.' Literally: 'Say your sleep talk after you go to sleep.' Used to dismiss absurd or unrealistic statements.
"If I win the lottery, I'll quit my job." "Don't talk nonsense."
That impossible plan is just nonsense.