from the horse's mouth

from the horse's mouth idiom
From a reliable source, on the best authority. For example, I have it from the horse's mouth that he plans to retire next month. Also put as straight from the horse's mouth, this expression alludes to examining a horse's teeth to determine its age and hence its worth. [1920s]

The American Heritage® Dictionary of Idioms by Christine Ammer. Copyright © 2003, 1997 by The Christine Ammer 1992 Trust. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

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