Valmiki Ramayana Aranya Kanda Sarga 4 Shloka 18
Original Shlokaअनुपस्थीयमानो मां स क्रुद्धो व्याजहार ह। इति वैश्रवणो राजा रम्भासक्तमुवाच ह।।3.4.18।।
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सः that, अनुपस्थीयमानः not being attended to, क्रुद्धः angry, माम् me, व्याजहार said, राजा king, वैश्रवणः Kubera, रम्भासक्तम् passionately attached to Rambha, इति like this, उवाच ह cursed.
When king Kubera saw me absent (from duty) as I was infatuated with Rambha, he got angry and cursed me.