Shiva Purana
अशुचेस्त्वग्निसंयोगाच्छुचित्वमपि जायते ॥ एवं शोध्यात्मसंसर्गान्न ह्यशुद्धः शिवो भवेत् ॥ ४५ ॥
The combination of the impure with fire also leads to purity. Thus one should purify himself by association with himself and not become impure and auspicious.
english translation
azucestvagnisaMyogAcchucitvamapi jAyate ॥ evaM zodhyAtmasaMsargAnna hyazuddhaH zivo bhavet ॥ 45 ॥
hk transliteration by Sanscript