Srimad-Bhagavatam: Canto 9 - Chapter 1 - Verse 26
Sanskrit:
तस्मिन् प्रविष्ट एवासौ सुद्युम्न: परवीरहा ।अपश्यत् स्रियमात्मानमश्वं च वडवां नृप ॥ २६ ॥
ITRANS:
tasmin praviṣṭa evāsausudyumnaḥ para-vīra-hāapaśyat striyam ātmānamaśvaṁ ca vaḍavāṁ nṛpa
Translation:
O King Parīkṣit, as soon as Sudyumna, who was expert in subduing enemies, entered the forest, he saw himself transformed into a female and his horse transformed into a mare.