Valmiki Ramayana Aranya Kanda Sarga 37 Shloka 19
Original Shlokaतस्य सा नरसिंहस्य सिंहोरस्कस्य भामिनी। प्राणेभ्योऽपि प्रियतरा भार्या नित्यमनुव्रता।।3.37.19।।
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सा भामिनी effulgent lady, सिंहोरस्कस्य of a lion's chest, तस्य his, नरसिंहस्य of a lion in the form of man, प्राणेभ्योपि more than his life, प्रियतरा dearer, भार्या wife, नित्यम् always, अनुव्रता loyal to him.
Beautiful Sita happens to be the wife of Rama who is like a lion among men. Rama has a broad chest like that of a lion. He loves Sita who is ever loyal to him, more than his life.