Shiva Purana
वह्निबीजं समुच्चार्य त्वादधीताग्निमासने ॥ योनिमार्गेण वा तद्वदात्मनः संमुखेन वा ॥ १५ ॥
After reciting the seed of fire, one should sit on the seat of the fire and study it. Either through the vagina or in front of the self.
english translation
vahnibIjaM samuccArya tvAdadhItAgnimAsane ॥ yonimArgeNa vA tadvadAtmanaH saMmukhena vA ॥ 15 ॥
hk transliteration by Sanscript