on faith, take it
Trust, accept without proof, as in I have no firm evidence that Bob's responsible for the errors—you'll just have to take it on faith. This idiom employs faith in the sense of “belief or confidence in something,” a usage dating from about 1300.
Words nearby on faith, take it
on duty,
on earth,
on easy street,
on edge,
on end,
on faith, take it,
on file,
on fire,
on foot,
on good terms,
on hand