What is the source of the prayer ending And the wisdom to know the difference?

The prayer that you speak of is one of several prayers of Saint Francis of Assisi who was born circa 1181AD and died 1226AD. Saint Francis was the founder of the Franciscan Order of Friars Minor although there are other "reformed" Orders and offshoots of that Order eg. The Order of Friars Minor Capuchin and The Order of Friars Minor Conventual and some Orders of nuns as well eg. The Poor Clares. The following is one several prayers attributed to Saint Francis: LORD, GRANT ME THE SERENITYTO ACCEPT THE THINGS I CANNOT CHANGE,THE COURAGE TO CHANGE THE THINGS I CANAND THE WISDOM TO KNOW THE DIFFERENCE.

Answer #2

If one does not have the wisdom to know the difference between the things he can and cannot change, he's likely to try changing the things that he cannot