<?php

$arr = array( array('id'=>1, 'email_id'=>'ok@gmail.com', 'password'=>'test'),
      array('id'=>2, 'email_id'=>'check@gmail.com', 'password'=>'test'), 
      array('id'=>3, 'email_id'=>'an@gmail.com', 'password'=>'pass'));

      $new_arr = array();
      foreach($arr as $k => $v) {
          if( is_array($arr[$k+1]) && $arr[$k]['password'] === $arr[$k + 1]['password'] )
              $new_arr[] = array($arr[$k], $arr[$k+1]);
          else if( in_array_recursive($arr[$k]['password'], $new_arr) === FALSE ) 
                  $new_arr[] = $v;
      }

      function in_array_recursive( $val, $arr) {
          foreach( $arr as $v ) {
              foreach($v as $m) {
                  if( in_array($val, $m ) )
                      return TRUE;      
              }
          }
          return FALSE;
      }

      print_r($new_arr);
?>

Array
(
    [0] => Array
        (
            [0] => Array
                (
                    [id] => 1
                    [email_id] => ok@gmail.com
                    [password] => test
                )

            [1] => Array
                (
                    [id] => 2
                    [email_id] => check@gmail.com
                    [password] => test
                )

        )

    [1] => Array
        (
            [id] => 3
            [email_id] => an@gmail.com
            [password] => pass
        )

)