Shiva Purana
ग्रीष्मे पंचाग्निमध्ये तु वर्षासु स्थंडिलेशयः ॥ शीते जलांतरस्थो हि कृतं चैव त्रिधा तपः ॥ ४० ॥
Standing in the midst of five fires during the summer, lying on the bare ground during rains and staying inside water during the winter I performed three-fold penance.
english translation
grISme paMcAgnimadhye tu varSAsu sthaMDilezayaH ॥ zIte jalAMtarastho hi kRtaM caiva tridhA tapaH ॥ 40 ॥
hk transliteration by Sanscript