Letters 94.49

On that basis, therefore, even consolation would be superfluous, since this also is a combination of the other two, as likewise are exhortation, persuasion, and even proof itself. For proof also originates from a well-ordered and firm mental attitude. But, although these things result from a sound state of mind, yet the sound state of mind also results from them; it is both creative of them and resultant from them.

Seneca, Letters to Lucilius 94.49, translated by Richard Mott Gummere