When Lord Hanuman Indulged in a very struggle with Ahiravana, he found out that it had been not possible to eliminate Ahiravana inside of a struggle, and there needs to be some magic formula about his Demise. Anjana executed intense prayers to Lord Shiva to hunt liberation from the curse, https://www.youtube.com/watch?v=ufkmD95y7fE&t=1s