I did not note in my journal where I originally found this quote. It seems that St. Francis has picked up on Jesus' words in Matthew, chapter six: "Therefore do not be anxious about tomorrow, for tomorrow will be anxious for itself." (6:34a)
Do not look forward to what may happen tomorrow; the same everlasting Father who cares for you today will take care of you tomorrow and everyday. Either He will shield you from suffering or He will give you unfailing strength to bear it. Be at peace, then, put aside all anxious thoughts and imaginations and say continually: The Lord is my strength and my shield; my heart has trusted in Him and I am helped...