Valmiki Ramayana Yuddha Kanda Sarga 91 Shloka 29
Original Shlokaसूतास्तेहयास्तत्ररथमूहुरविक्लबाः ।।6.91.29।। मण्डलान्यभिधावन्तस्तदद्भुतमिवाभवत् ।
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तत्र there, असूताः charioteer, ते, हयाः horses, अविक्लबाः without being perplexed मण्डलानि in circles, अभिधावन्तः as they went forward, रथम् chariot, ऊहुः, तत् then, अद्भुतमिव wonderful, अभवत् seemed
There, though there was no charioteer, the horses went round in circles and as they went forward it was wonderful.