Shiva Purana
रं वह्नयेति स्वाहेति मध्ये हुत्वाहुतित्रयम् ॥ सर्पिषा वा समिद्भिर्वा परिषेचनमाचरेत् ॥ २६ ॥
In the middle of the sacrificial fire one should chant the mantra rām vahṇaya and svāhā. Sprinkle with butter or with sacrificial fires.
english translation
raM vahnayeti svAheti madhye hutvAhutitrayam ॥ sarpiSA vA samidbhirvA pariSecanamAcaret ॥ 26 ॥
hk transliteration by Sanscript