Valmiki Ramayana Aranya Kanda Sarga 48 Shloka 4
Original Shlokaयेन वैश्रवणो राजा द्वैमात्रः कारणान्तरे। द्वन्द्वमासादितः क्रोधाद्रणे विक्रम्य निर्जितः।।3.48.4।।
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येन by whom, कारणान्तरे for some other reason, क्रोधात् in anger, द्वन्द्वम् duel, आसादितः took place, द्वैमात्रः stepmother, वैश्रवणः राजा king Vaisravana, रणे in war, विक्रम्य with my prowess, निर्जितः was defeated.
For some reason or other a duel took place between me and king Kubera. With my prowess, I defeated him in the duel.