Expression of the Fortnight - 11

STRAIGHT FROM THE HORSE'S MOUTH

If you hear something straight from the horse's mouth or you know that a piece of information has come straight from the horse's mouth then you know that you can believe it because it has come from an authoritative or dependable source.

"Are you sure John is leaving the company?"
"Definitely, I heard it straight from the horse's mouth!"
(John told you himself)

"This comes straight from the horse's mouth so it has to be believed!"