set (one's) mind to rest
set (one's) mind to rest
To assuage or relieve one's worry, anxiety, dread, fear, etc. I know you're anxious to hear how your father is doing after the surgery, so let me set your mind to rest: he's going to make a full recovery. That bonus really set my mind at rest about these debts.
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.