sleep on it : that means to not make an immediate decision about a plan or idea, but to wait until the next day in order to have more time to think about it.
Examples:
1. I'll get back to you tomorrow. I have to sleep on it.
2. You don't have to give me your decision now. Sleep on it, and let me know tomorrow.
Replies
That exactly what men usually do!
hi
When my mother told me about someone wanted my hand, I refused without sleeping on it.