In De finibus, the Stoic Chrysippus explains:
For our individual natures are parts of the whole cosmos. And this is why the end may be defined as life in accordance with nature, or in other words, according to our own human nature as well as that of the cosmos, a life in which we refrain from every action forbidden by the law common to all things, that is to say, the right reason which pervades all things, and is identical with this Zeus, lord and ruler of all that is (Lives, 7. 87-88)