Valmiki Ramayana Yuddha Kanda Sarga 85 Shloka 19

महायशः of great fame, वीर hero, सरथस्य with that chariot, अन्तरिक्षे sky, चरतः going, तस्य his, गतिः movement, अभ्रसम्प्लवे coursing through clouds, सूर्यस्येव, like sun न ज्ञायते cannot be known

When he moves in his chariot in the sky like the Sun coursing through clouds is difficult to know.