Shiva Purana
न तत्तपोभिरत्युग्रैर्न च सर्वैर्महामखैः ॥ गच्छेच्छिवपुरं दिव्यं मुक्त्वा भक्तिं शिवात्मकम् ॥ ५३ ॥
Without this none can go to the divine city of Śiva through any sort of penances.
english translation
na tattapobhiratyugrairna ca sarvairmahAmakhaiH ॥ gacchecchivapuraM divyaM muktvA bhaktiM zivAtmakam ॥ 53 ॥
hk transliteration by Sanscript