Shiva Purana
तेनाग्निमन्त्रपूतात्मा क्षत्त्रियो ब्राह्मणो भवेत् ॥ विधितो ब्राह्मणो भूत्वा याजकस्तु प्रजायते ॥ १५ ॥
By this a kshatriya whose soul is purified by the mantra of fire becomes a brahmin A priest is born a brahmin according to the prescribed rituals.
english translation
tenAgnimantrapUtAtmA kSattriyo brAhmaNo bhavet ॥ vidhito brAhmaNo bhUtvA yAjakastu prajAyate ॥ 15 ॥
hk transliteration by Sanscript