/**
 * Validate IP Address For A Given User
 */
add_filter( 'authenticate', function( $user )
{
    // Adjust to your needs:
    $allowed_ip             = '127.0.0.1';
    $ip_restricted_user_id  = 1;

    // Current user IP address
    $current_user_ip = isset( $_SERVER['REMOTE_ADDR'] ) ? $_SERVER['REMOTE_ADDR'] : null;

    // Nothing to do for valid IP address
    if( $current_ip === $allowed_ip )
        return $user;

    // Nothing to do for users that are not IP restricted
    if(
           $user instanceof WP_User
        && $user->ID > 0
        && $ip_restricted_user_id != $user->ID
    )
        return $user;

    // Add an 'Invalid IP address' error
    if( is_wp_error( $user ) )
        $user->add(
            'invalid_ip',
            sprintf(
            '<strong>%s</strong>: %s',
            esc_html__( 'ERROR', 'mydomain' ),
            esc_html__( 'IP address is invalid.', 'mydomain' )
        )
    );
    // Create a new 'Invalid IP address' error
    else
        $user = new WP_Error(
            'invalid_ip',
            sprintf(
                '<strong>%s</strong>: %s',
                esc_html__( 'ERROR', 'mydomain' ),
                esc_html__( 'IP address is invalid.', 'mydomain' )
            )
        );

    return $user;
}, 100 );

add_filter( 'authenticate', 'wp_authenticate_username_password',  20, 3 );
add_filter( 'authenticate', 'wp_authenticate_email_password',     20, 3 );
add_filter( 'authenticate', 'wp_authenticate_spam_check',         99    );