2 Corinthians 12:9 – 10
New International Version (NIV)
9 But he said to me, “My grace is sufficient for you, for my power is made perfect in weakness.” Therefore I will boast all the more gladly about my weaknesses, so that Christ's power may rest on me. 10 That is why, for Christ's sake, I delight in weaknesses, in insults, in hardships, in persecutions, in difficulties. For when I am weak, then I am strong.
From BibleGateway.com: http://www.biblegateway.com/passage/?search=2 Corinthians 12:9-10&version=NIV