Excerpt from The Great Treatise (繫辭上) an appendix to the Book of Changes (周易)

一陰一陽之謂道，繼之者善也，成之者性也。

"One time Yin, one time Yang, this is what is called the Dao. Those that go on with it are virtuous, those that accomplish it are natural."

Unless noted otherwise, all quotations of classical texts come from the Chinese Text Project