Gainsay

We cannot gainsay that he is honest.

Source: tatoeba (283931)

The contumacious student dared to gainsay his teacher.

Source: tatoeba (4995874)

Now, however, that they had received the command to rest and sleep (and to gainsay the Father's commands was a thing that would never have entered their minds), they were willing enough to obey, and had hardly laid themselves down before they fell into a deep slumber, from which neither awoke until the light of day had long been shining upon the world, and the Father stood beside them bidding them rise and follow him.

Source: tatoeba (11031913)

[…]vve are able with playne demonſtration to proue, and vvith reaſon to perſvvade that in tymes paſt our fayth vvas alike, that then vve preached thinges correſpondent vnto the forme of faith already publiſhed of vs, ſo that none in this behalfe can repyne or gayneſay vs.

Source: wiktionary