Class 'MongoDB\Driver\Manager' not found

Hello guys I'm integrating mongodb with laravel. I'm following this linkjenssegers/laravel-mongodb. I'm successful at integrating the mongodb. But when I run the code it throws me this error

FatalErrorException in Client.php line 56: Class 'MongoDB\Driver\Manager' not found

Here is the code

Controller app/Http/Controller/NewController

<?php

namespace App\Http\Controllers;

use Illuminate\Http\Request;

use App\Http\Requests;

use App\User;

class NewController extends Controller
{
    //
    public function index(){
        $var = User::all();
        var_dump($var);
    }
}

and the user.php by default provided by larvel when we make the project

<?php

namespace App;

use Illuminate\Foundation\Auth\User as Authenticatable;
use Jenssegers\Mongodb\Eloquent\Model as Eloquent;

class User  extends Eloquent 
{
    /**
     * The attributes that are mass assignable.
     *
     * @var array
     */
    protected $collection = 'users_collection';
    protected $fillable = [
        'name', 'email', 'password',
    ];

    /**
     * The attributes excluded from the model's JSON form.
     *
     * @var array
     */
    protected $hidden = [
        'password', 'remember_token',
    ];
}

Please tell me why am I facing this error.

Phpinfo --> mongodb section is coming. Here is a screen shot phpinfo

via Chebli Mohamed