Valmiki Ramayana Ayodhya Kanda Sarga 8 Shloka 3
Original Shlokaमनसा प्रहसामि त्वां देवि दुःखार्दिता सती। यच्छोचितव्ये हृष्टाऽसि प्राप्येदं व्यसनं महत्।।2.8.3।।
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देवि O queen, महत् great, इदम् this, व्यसनम् misfortune, प्राप्य having obtained, शोचितव्ये (at a time) one should feel sad, यत् since, हृष्टा असि you are rejoicing, दु:खार्दिता सती although afflicted with grief, त्वाम् about you, मनसा in my mind, प्रहसामि I am laughing.
O queen at a time when this great misfortune has befallen you, you are rejoicing instead of feeling miserable. I am indeed laughing at you at heart.