As the mistake was completed from the god Indra, he grants Hanuman a want that his entire body can be as sturdy as Indra's Vajra, Which his Vajra can also not hurt him. Together with Indra other gods have also granted him needs: the God Agni granted Hanuman a desire https://hindu-temples-in-adelaide.mystrikingly.com/blog/hanuman-temples-and-hindu-worship-in-adelaide