class User extends ActiveRecord {
public static $table = "users";
public static $key = "user_id";

public static function login($email, $password) {
$users=self::getAll(" WHERE email = '$email' AND password = '$password' LIMIT 1");
    print_r($users);
}

<?php

    abstract class ActiveRecord {
    public static function getAll($filter="") {
    $instance = Database::getInstance();
    $conn = $instance->getConnection();

    $pdo = $conn->prepare("SELECT * FROM ".static::$table." ".$filter);
    $pdo->execute();


    $res = $pdo->fetchAll(PDO::FETCH_CLASS, get_called_class());

    return $res;


}

<?php
include("admin/config.php");

if (isset($_POST['inputEmail']) && !empty($_POST['inputEmail']) &&
isset($_POST['inputPassword']) && !empty($_POST['inputPassword'])) {

$email = $_POST['inputEmail'];
$password = $_POST['inputPassword'];

$user = User::login($email, $password);
}