little bird told one, a
A source one cannot or will not identify gave this information, as in How did you learn they were getting a divorce?—Oh, a little bird told me. Versions of this idiom date from ancient times and appear in numerous proverb collections.
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.