take as gospel
Also, take for gospel. Believe absolutely, regard as true, as in We took every word of his as gospel, but in fact he was often mistaken. This idiom, first recorded in 1496, uses gospel in the sense of the absolute truth. Also see gospel truth.
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.