Letters 66.32

Hence it is without reason that both these things distract and sting the spirit; the one is not worthy of joy, nor the other of fear. It is reason alone that is unchangeable, that holds fast to its decisions. For reason is not a slave to the senses, but a ruler over them. Reason is equal to reason, as one straight line to another; therefore virtue also is equal to virtue. Virtue is nothing else than right reason. All virtues are reasons. Reasons are reasons, if they are right reasons. If they are right, they are also equal.

Seneca, Letters to Lucilius 66.32, translated by Richard Mott Gummere