Tell the truth and shame the devil!
The preacher Hugh Latimer recorded this as a 'common saying' as early as 1555, in his Twenty Seven Sermons:
"There is a common saying amongst vs, Say the truthe and shame the diuel."
Shakespeare also used the expression in Henry IV. Part I, 1597:
And I can teach thee, coz, to shame the devil
By telling truth: tell truth and shame the devil.
If thou have power to raise him, bring him hither,
And I'll be sworn I have power to shame him hence.
O, while you live, tell truth and shame the devil!