The original quote is attributed to Phillip Brooks 1835 - 1893(US Clergyman) The original quote: "O, do not pray for easy lives. Pray to be stronger men! Do not pray for tasks equal to your powers. Pray for powers equal to your tasks! Then the doing of your work shall be no miracle. But you shall be a miracle. Every day you shall wonder at yourself, at the richness of life which has come to you by the grace of God."
It was Bruce Lee who actually said that. John F. Kennedy's statement was also similar but a bit different like, "Do not pray for easy lives, but pray to be stronger men". Bruce Lee had another nice quote, "The mind is like a fertile garden where anything that is planted, flowers or weeds, grows."