Seneca · On the approaches to philosophy
Letters 108.11
We talk much about despising money, and we give advice on this subject in the lengthiest of speeches, that mankind may believe true riches to exist in the mind and not in one’s bank account, and that the man who adapts himself to his slender means and makes himself wealthy on a little sum, is the truly rich man; but our minds are struck more effectively when a verse like this is repeated:
He needs but little who desires but little.
or,
He hath his wish, whose wish includeth naught Save that which is enough.
Seneca, Letters to Lucilius 108.11, translated by Richard Mott Gummere