Once on being instigated by Narada, Hanuman unknowingly insulted Vishwamitra. This happened when Hanuman greeted all the sages in Rama’s court but didn’t greet Vishwamitra because he wasn’t a saint by birth. Vishwamitra felt offended and ordered Rama to issue a death sentence for Hanuman. The death sentence was executed, but none of the arrows or even the brahmastra could harm Hanuman. This was because Hanuman kept chanting Rama’s name.