add_filter( 'wp_new_user_notification_email' , 'edit_user_notification_email', 10, 3 );

function edit_user_notification_email( $wp_new_user_notification_email, $user, $blogname ) {

    $message = wp_login_url() . "rn";
    $message .= sprintf(__( 'Username: %s' ), $user->user_login ) . "rn";
    $message .= sprintf(__( 'Password: %s' ), $user->user_pass );
    $wp_new_user_notification_email['message'] = $message;

    return $wp_new_user_notification_email;

}