put (one) on (one's) honor
1. To allow one to be unsupervised with the understanding that one will act ethically, morally, or according to the rules or the law. I have to leave the classroom for a little while, so I'm putting you all on your honor to complete your test without cheating. Don't you think it's a little foolhardy putting her on her honor not to steal from you when she's only been working in the store for a couple of weeks?
2. To treat one with the assumption that one will speak with the utmost sincerity, honesty, or integrity. I'm putting you on your honor to tell me the truth, John—did you steal the money? Are you willing to go up on the witness stand, be put on your honor, and tell the courtroom what really happened?