take at word
take somebody at their word
to decide to believe exactly what someone tells you, even if it does not seem likely to be true When he said he'd give me a job, I took him at his word and turned up the next day at his office.
take at (someone's) word
To be convinced of another's sincerity and act in accord with his or her statement: We took them at their word that the job would be done on time.