Valmiki Ramayana Aranya Kanda Sarga 46 Shloka 4

अतिबलः mighty Ravana, वने in the forest, भ्रातृभ्याम् with both brothers, रहिताम् in the absence of, ताम् them, चन्द्रसूर्याभ्याम् by both Sun and Moon, सन्ध्याम् in the evening twilight, महत् great, तमः इव like darkness, आससाद reached.

Mighty Ravana approached Sita deprived of both the brothers, Like darkness encompasses the evening twilight in the absence of the Sun and the Moon.