 तपसा निर्दहेल्लोकान्क्रुद्धो वा निर्दहेदपि।

सर्वधातिप्रवृद्धोऽसौ रावणो राक्षसाधिपः  ॥
  
 "The demon king is rich in asceticism. He can burn the whole world with the power of his penance. In spite of Sitas anger he was not burntHanuman gives the reason for Ravanas survival. 