Do you not know? Have you not heard?
The Lord is the everlasting God, the Creator of the ends of the earth. He will not grow tired or weary, and his understanding no one can fathom.
Isaiah 40:28 (NIV)
Even the youths shall faint and be weary, and the young men shall utterly fall:
But they that wait upon the Lord shall renew their strength; they shall mount up with wings as eagles; they shall run, and not be weary; and they shall walk, and not faint.