Laravel- Add after hook in request file. Reference: https://goo.gl/8BhhCB

laravel-add-after-in-request.php

<?php
/**
 * Get the validator instance for the request and 
 * add attach callbacks to be run after validation 
 * is completed.
 *
 * @return \Illuminate\Contracts\Validation\Validator
 */
protected function getValidatorInstance()
{   
    return parent::getValidatorInstance()->after(function($validator){
        // Call the after method of the FormRequest (see below)
        $this->after($validator);
    });
}
/**
 * Attach callbacks to be run after validation is completed.
 * 
 * @param  \Illuminate\Contracts\Validation\Validator $validator
 * @return callback
 */
public function after($validator)
{
    if ($this->somethingElseIsInvalid()) {
        $validator->errors()->add('field', 'Something is wrong with this field!'); 
    }
}