Srimad-Bhagavatam: Canto 4 - Chapter 1 - Verse 18
Sanskrit:
तत्तस्य चाद्भुतं कर्म विचक्ष्य परमर्षय: ।नामधेयं ददुस्तस्मै विजिताश्व इति प्रभो ॥ १८ ॥
ITRANS:
tat tasya cādbhutaṁ karmavicakṣya paramarṣayaḥnāmadheyaṁ dadus tasmaivijitāśva iti prabho
Translation:
My dear Lord Vidura, when the great sages observed the wonderful prowess of the son of King Pṛthu, they all agreed to give him the name Vijitāśva.