Shiva Purana
अपावनानि सर्वाणि वह्निसंसर्गतः क्षणात् ॥ पावनानि भवन्त्येव तस्माद्यः पावकः स्मृतः॥ ६५॥
All unholy things become pure the moment they come into contact with fire. Therefore fire is called Purifier,
english translation
apAvanAni sarvANi vahnisaMsargataH kSaNAt ॥ pAvanAni bhavantyeva tasmAdyaH pAvakaH smRtaH॥ 65॥
hk transliteration by Sanscript