Praying for God to soften the hearts of atheist friends is the most important thing Christian can do for non-believers, says famed evangelist the Rev. Billy Graham, who also encourages believers to be a "witness to Jesus' peace and joy."

In a question-and-answer column published Monday on the Billy Graham Evangelistic Association website, Graham was asked what Christians can do to encourage their atheist friends to seek salvation in Jesus Christ.

"My best friend and I enjoy each other's company, but I'm a Christian and he says he's an atheist. I've tried to argue with him, but he just laughs and says I ought to grow up and forget about God. How can I win him over?" the person asked.

Graham responded by saying, "you can't win him over by yourself" and that part of the effort must include God, since "He can conquer even the most stubborn heart.

"And that's why the most important thing you can do for your friend is to pray for him, asking God to convict him of his sin and his pride and convince him of his need for Christ," wrote Graham.

"Pray also that your life will be a witness to him — a witness to Christ's peace and joy. People may argue with what we say — but they can't argue with the reality of a life that's been transformed by Christ."