Ramayana
माहेश्वरे प्रवृत्ते तु यज्ञे पुम्भिः सुदुर्लभे । वरांस्ते लब्धवान्पुत्रः साक्षात्पशुपतेरिह ॥ 7-25-9 ॥
When that sacrifice sacred to Maheshvara, which is most difficult for men to perform, had been undertaken, your son obtained these boons here directly from Pashupati himself.
english translation