只有变量应该通过引用php传递

I checked similar questions here but it couldn't solve my problem. I'm creating a php user registration form and when I try to register I get this error: Strict standards: Only variables should be passed by reference in F:\wamp64\www\loginegister.php on line 14

I tried it on PHP version 5.6 and 7.0 but the error is the same.

Line 14 is this:

$stmt->bindParam(':password', password_hash($_POST['password'],  PASSWORD_BCRYPT));

Here is my entire code:

<?php
$server = 'localhost';
$username = 'root';
$password = 'root';
$database = 'auth';

try{
  $conn = new PDO("mysql:host=$server;dbname=$database;", $username, $password);
} catch(PDOException $e) {
  die( "Connection failed: " . $e->getMessage());
}

$message = '';

if(!empty($_POST['email']) && !empty($_POST['password'])):

  $sql = "INSERT INTO users (email, password) VALUES (:email, :password)";
  $stmt = $conn->prepare($sql);

  $stmt->bindParam(':email', $_POST['email']);
  $stmt->bindParam(':password', password_hash($_POST['password'], PASSWORD_BCRYPT));

  if( $stmt->execute()):
    $message = 'Successfully created new user';
  else:
    $message = 'Sorry there must have been an issue creating your account';
  endif;

endif;

?>

Any help is appreciated, thanks.

try

$pass = ':password';
$phash = password_hash($_POST['password'],  PASSWORD_BCRYPT);

$stmt->bindParam($pass, $phash);