While in quarantine in Japan, my friends have been sending me photo's of my horse "Ted".  This got me wondering about what Ted would be thinking and what might he be wanting to say to us.  This reminded me of the idiom "from the horse's mouth".  Meaning information from the highest authority possible.

This is not a rumour or gossip but facts.

A: I heard it from the horse's mouth.
B: Really?
A: If you don't believe me, then go and ask him yourself.

In a business setting this might be a change of direction or plan, which has not been announced in full yet.   It might only be known by a few managers who are aware of the change, it might start off as gossip but as soon as the Chairman announces the change, it is a fact from the horse's mouth.

A recent example in the UK, the second lockdown information was leaked by the newspapers, however, when Boris Johnson confirm it as fact, the information came from the horse's mouth.