James 1:2-4 (New International Version)

Trials and Temptations
 2 Consider it pure joy, my brothers and sisters, whenever you face trials of many kinds, 3 because you know that the testing of your faith produces perseverance. 4 Let perseverance finish its work so that you may be mature and complete, not lacking anything.

From BibleGateway.com: http://www.biblegateway.com/passage/?search=james 1:2-4&version=NIV