How to answer critics
English evangelist George Whitefield knew that what he was doing was honoring to the Lord, which kept him from discouragement when his enemies falsely accused him. At one point in his ministry, Whitefield received a vicious letter accusing him of wrongdoing. His reply was brief and courteous: “I thank you heartily for your letter. As for what you and my other enemies are saying against me, I know worse things about myself than you will ever say about me. With love in Christ, George Whitefield.” He didn't try to defend himself. He was much more concerned about pleasing the Lord.
Source: Daily in the Word, May 27, 2008