Matthew 17:20
New International Version (NIV1984)
20 He replied, “Because you have so little faith. I tell you the truth, if you have faith as small as a mustard seed, you can say to this mountain, ‘Move from here to there’ and it will move. Nothing will be impossible for you.”
From BibleGateway.com: http://www.biblegateway.com/passage/?search=matthew 17:20&version=NIV