— Marcus Aurelius Emperor of Ancient Rome 121 - 180
No printed sources exist for this prior to 2009, and this seems to have been an attribution which arose on the internet, as indicated by web searches and rationales provided at "Marcus Aurelius and source checking" at Three Shouts on a Hilltop (14 June 2011) http://threeshoutsonahilltop.blogspot.com/2011/06/marcus-aurelius-and-source-checking.html
This quote may be a paraphrase of Meditations, Book II:
Since it is possible that thou mayest depart from life this very moment, regulate every act and thought accordingly.
But to go away from among men, if there are gods, is not a thing to be afraid of, for the gods will not involve thee in evil;
but if indeed they do not exist, or if they have no concern about human affairs, what is it to me to live in a universe devoid of gods or devoid of Providence?
But Gods there are, undoubtedly, and they regard human affairs; and have put it wholly in our power, that we should not fall into what is truly evil