Ephesians 2:8-9:

For by grace are ye saved through faith, and that not of yourselves: it is the gift of God:
Not of works, lest any man should boast.

See also:

You Have Faith
Faith Is a Gift from God
What Mark 11:22 Really Means
What Galatians 2:20 Really Means
What Are the Differences Between the Gift of Faith, the Gifts of Healings, and the Working of Miracles?
Is Faith a Force?
How Can Faith Be Both a Fruit of the Spirit and a Gift of the Spirit?
Does Faith Come from Your Spirit, Your Mind or Somewhere Else?
Does God Heal You in Response to Your Faith?
Objection: Mark 16:18 Does Not Say, “They Shall Recover IF They Have Enough Faith,” Yet Faith Healers Blame the Sick for Not Believing
Objection: Faith Is a Gift from God, Not Something You Work up Yourself