with assurance

See: fairly
References in classic literature ?
Bennet's acknowledgments he briefly replied, with assurance of his eagerness to promote the welfare of any of his family; and concluded with entreaties that the subject might never be mentioned to him again.
He spoke slowly, with assurance that he would be listened to, and he looked only at the person with whom he was conversing.
He therefore dismissed her with assurances that he would very soon remove her out of the reach of that obloquy she had incurred; concluding with some additional documents, in which he recommended repentance, saying, "Consider, child, there is one still to reconcile yourself to, whose favour is of much greater importance to you than mine.