on good authority

on good authority — из достоверных источников, по достоверным сведениям

have (got) sth on good authority (be able to believe sth because you trust the person who gave you the information) — знать из достоверных источников, по достоверным сведениям

Example 1: I have it on good authority that Jill is going to resign.

Example 2: ...

see also
[из первых рук]