Shiva Purana
आराधितः कियत्कालं न प्रसन्नो हरो यदा॥ तदा चान्यत्तपश्चक्रे प्रासादार्थे शिवस्य सः॥ २॥
Though the worship continued for a long time, Śiva was not delighted. Then Rāvaṇa performed another penance to delight Śiva.
english translation
ArAdhitaH kiyatkAlaM na prasanno haro yadA॥ tadA cAnyattapazcakre prAsAdArthe zivasya saH॥ 2॥
hk transliteration by Sanscript