View file vendor/illuminate/database/Eloquent/Relations/Pivot.php

<?php

namespace Illuminate\Database\Eloquent\Relations;

use Illuminate\Database\Eloquent\Model;
use Illuminate\Database\Eloquent\Relations\Concerns\AsPivot;

class Pivot extends Model
{
    use AsPivot;

    /**
     * The attributes that aren't mass assignable.
     *
     * @var array
     */
    protected $guarded = [];
}