D. R. Van Sickle wrote the hymn "All hail to Thee, Immanuel" in 1910 when he was an unbeliever to show that non-Christians could write Christian hymns. Years later after this hymn was published, he was sitting in church, heard the choir sing his hymn and by the grace of God was converted.
Music in Evangelism: And Stories of Famous Christian Songs by Phillip Stanley Kerr, (Glendale, Calif: Gospel Music Publishers, 1939)