Valmiki Ramayana Yuddha Kanda Sarga 69 Shloka 29
Original Shlokaहयमुच्चैश्श्रवःप्रख्यंश्वेतंकनकभूषणम् । मनोजवंमहाकायमारुरोहनरान्तकः ।।6.69.29।।
1 source checked for this shloka
नरान्तकः Naranthaka, उच्छैःश्रवःप्रख्यम् Uchaisrava (horse evolved in churning of the milky ocean), श्वेतम् white, कनकभूषणम् decked in gold, मनोजवम् swift as thought in speed, महाकायम् huge, हयम् horse, आरुरोह mounted.
Naranthaka, mounted on Uchaisrava, the white horse, decked in gold, was swift as thought in speed.