The Little Book of Bathroom Philosophy : Daily Wisdom from the Greatest Thinkers (2004) by Gregory Bergman, p. 50
The original, full quote reads "Quantum in te crescit amor, tantum crescit pulchritudo; quia ipsa charitas est animae pulchritudo," and was fully translated as "Since love grows within you, so beauty grows. For love is the beauty of the soul." Here Augstine points out the inherent beauty that takes root within us when we love.
Attributed to Pierre de Beaumarchais, a French playwright, this quote is actually unsourced and is not found in his plays. He was also a social satirist, and while he may have said the above quote, it doesn't seem to quite match the tone of his work.