Ramayana
ततस्तेनैव कोपेन दशग्रीवः सहानुजः । चिकीर्षुर्दुष्करं कर्म तपसे धृतमानसः ॥ 7-9-46 ॥
Then, on account of that very wrath, Dashagriva, together with his younger brothers, his mind fixed upon austerity, resolved to perform a feat hard to accomplish.
english translation