Letters 85.17

Then, again, we should see to it that two principles which ought to be tested separately should not be confused. For the conclusion is reached independently that that alone is good which is honourable, and again independently the conclusion that virtue is sufficient for the happy life. If that alone is good which is honourable, everyone agrees that virtue is sufficient for the purpose of living happily; but, on the contrary, if virtue alone makes men happy, it will not be conceded that that alone is good which is honourable.

Seneca, Letters to Lucilius 85.17, translated by Richard Mott Gummere