Valmiki Ramayana Yuddha Kanda Sarga 75 Shloka 42

सन्नह्यमानानाम् as they were preparing, सिंहनादम् leonine, कुर्वताम् doing, तेषाम् by them, राक्षसेन्द्राणाम् Rakshasa leaders, शर्वरी night, रौद्रीव Rudra's, समपद्यत came upon.

As the Rakshasa leaders were preparing (for attack) and emitting leonine roar, night came upon like the night of Rudra (night of final dissolution).