Shiva Purana
आग्नेयं वाथ वा मांत्रं कुर्यात्स्नानं शिवेन वा ॥ शिवचिंतापरं स्नानं युक्तस्यात्मीयमुच्यते ॥ १४ ॥
Or he shall take the self-bath. That is, one shall repeat the name Śiva. That bath wherein Śiva is remembered is called the self-bath of a Yogin.
english translation
AgneyaM vAtha vA mAMtraM kuryAtsnAnaM zivena vA ॥ zivaciMtAparaM snAnaM yuktasyAtmIyamucyate ॥ 14 ॥
hk transliteration by Sanscript