Ravana, commanded Prahastha to question who the Vanara is. Is it the Nandi (the bull) who cursed Ravana earlier has come in this form? Or is it Bana , the demon (Son of Bali). Quesiton who it is.
Prahastha started enquiring Hanuman “ Oh Vanara! Who are you? Are you sent by Indira or Varuna (Lord of Rains) or Kubera (Lord of Riches ) or Yama (Lord of Death) or sent by Vishnu. Don’t fear, tell us the truth. You might survive. Else we will kill you”
Hanuman replied “ Im not the one sent by any of the one whom you mentioned. This is my form by birth. I just tried protecting myself , my body and ended up killing all the demons. Nothing has the power to bind me. Even Brahmastra cannot bind me forever. This is the boon given by Lord Brahma itself to me. Even that got released and I still came here to see Ravana. Im a messenger from Lord Rama. I will tell you beneficial words. Listen to it”