Valmiki Ramayana Sundara Kanda Sarga 4 Shloka 12
Original Shlokaशुश्राव जपतां तत्र मन्त्रान् रक्षोगृहेषु वै।।5.4.12।। स्वाध्यायनिरतांश्चैव यातुधानान् ददर्श सः। रावणस्तवसंयुक्तान् गर्जतो राक्षसानपि।।5.4.13।।
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तत्र there, रक्षोगृहेषु in the demons' houses, जपताम् of those chanting, मन्त्रान् sacred (verses) words, शुश्राव heard, सः he, स्वाध्यायनिरतान् of those engaged in the study of Vedas continuously, यातुधानान् of demons, ददर्श saw, रावणस्तवसंयुक्तान् those engaged in the eulogy of Ravana, गर्जतः of those shouting, राक्षसानपि even the demons, ददर्श saw.
He heard chantings of sacred verses in the houses of demons engaged in the study of the vedas. And heard demons singing loudly the eulogy of Ravana.