Shiva Purana
अथ रुद्रः पिप्पलादोऽश्वत्थमूले महाप्रभुः ॥ तताप सुचिरं कालं लोकानां हितकाम्यया॥ ६३॥
Then Rudra, the great lord in the form of Pippalāda, performed a penance for a long time at the foot of the fig tree, with a desire to bestow benefit on the worlds.
english translation
atha rudraH pippalAdo'zvatthamUle mahAprabhuH ॥ tatApa suciraM kAlaM lokAnAM hitakAmyayA॥ 63॥
hk transliteration by Sanscript