God grant me the serenity to accept the things I cannot change;
courage to change the things I can;
and wisdom to know the difference.
The Serenity Prayer has traditionally been ascribed to Protestant theologian Reinhold Niebuhr, who wrote it in the early 1940s. New research has cast doubt on this, because similarly worded prayers have been found from the late 1930s, and credit was not given to him then. However, I think that everyone would agree that it was Niebuhr's version that is the best and most famous.
"The prayer is now ubiquitous, on mugs and greeting cards and embroidered pillows, sometimes with Niebuhr's name attached. But it is possible to find attributions ranging from Aristotle to St. Augustine to Francis of Assisi."
http://www.nytimes.com/2008/07/11/us/11prayer.html?_r=1&hp&oref=login