The one who practices sin is of the devil, because the devil has been sinning from the very start. This is why the Son of God was revealed, to destroy the works of the devil.
KJV
He that committeth sin is of the devil; for the devil sinneth from the beginning. For this purpose the Son of God was manifested, that he might destroy the works of the devil.
ASV
he that doeth sin is of the devil; for the devil sinneth from the beginning. To this end was the Son of God manifested, that he might destroy the works of the devil.