swear blind...

swear blind

To make a very serious, solemn pledge, especially that one is telling the truth. Janet has sworn blind that she wasn't the one to betray me, and I believe her.
See also: blind, swear
Farlex Dictionary of Idioms.

swear ˈblind (that)...

(informal) say that something is definitely true: She swore blind that she had not taken the money, and I believe her.
See also: swear
Farlex Partner Idioms Dictionary
See also:
  • give (one) (one's) head
  • give head
  • give somebody their head
  • give someone their head
  • 1FTR
  • drive (one) out of office
  • force (one) out of office
  • force out of office
  • cooking for one
  • as one door closes, another opens