believe (something) of (someone)
To accept that a statement about someone is true. I can't believe these lies of Cheryl—I have always known her to be a very reputable businesswoman.
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.
believe something of someone
to accept a statement about someone as truth. What a terrible thing for Jill to do. I can't believe it of her. I can believe anything of Max. He's such a conniving person.
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs. © 2002 by The McGraw-Hill Companies, Inc.