Shiva Purana
इत्थं भक्त्या शिवं शैवो यः साधयति साधकः ॥ तस्येहामुत्र दुष्प्रापं न किंचिदपि विद्यते ॥ २३ ॥
Nothing is inaccessible in this world or the next to him who is a devotee of Śiva and who is an aspirant practising the mantra of Śiva thus with devotion.
english translation
itthaM bhaktyA zivaM zaivo yaH sAdhayati sAdhakaH ॥ tasyehAmutra duSprApaM na kiMcidapi vidyate ॥ 23 ॥
hk transliteration by Sanscript