I have it on good authority

Origin

The very notion of "authority" stretches back to the Latin auctoritas, encompassing ideas of influence, command, and reliable advice. When it first entered English in the 14th century, it carried the weight of legal power and moral right. But by the 17th century, its meaning broadened: an "authority" also became a person whose word you could trust, a reliable font of knowledge. So, when someone declares "I have it on good authority," they're not just saying they heard a rumor; they're invoking a long-standing tradition of valuing information that comes from a source whose standing, expertise, or position lends indisputable credibility. It's an assertion that the news isn't just true, but comes from someone who knows.