Valmiki Ramayana 6.18.9
अवध्यः सर्वभूतानाम् गन्धर्वोरगपक्षिणाम् ।राजपुत्र दशग्रीवो वरदानात्स्वयम्भुवः॥
avadhyaḥ sarvabhūtānām gandharvoragapakṣiṇām |rājaputra daśagrīvo varadānātsvayambhuvaḥ ||
Our plain-language meaning of this verse is waiting for scholar review.
Open in the book