Valmiki Ramayana Sundara Kanda Sarga 59 Shloka 3
Original Shlokaतपसा निर्दहेल्लोकान्क्रुद्धो वा निर्दहेदपि। सर्वधातिप्रवृद्धोऽसौ रावणो राक्षसाधिपः ॥ 5.59.3 ॥
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सर्वधा ever, अतिप्रवृद्ध: rich in asceticism, असौ he is, राक्षसाधिपः demon king, तपसा his penance, लोकान् in the world, निर्दहेत् can burn, कुद्धो वापि even though angry, निर्दहेदपि not burnt
"The demon king is rich in asceticism. He can burn the whole world with the power of his penance. In spite of Sita's anger he was not burnt(Hanuman gives the reason for Ravana's survival).