Valmiki Ramayana Ayodhya Kanda Sarga 18 Shloka 23
Original Shlokaअतिसृज्य ददानीति वरं मम विशांपतिः। स निरर्थं गतजले सेतुं बन्धितुमिच्छति।।2.18.23।।
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स: विशांपति that king, ददानि इति saying 'I shall give you', मम to me, वरम् two boons, अतिसृज्य having bestowed, गतजले at a place where the water has drained, सेतुम् dam, निरर्थम् in vain, बन्धितुम् to construct, इच्छति wishes.
The king bestowed on me boons saying, 'I shall grant you two boons'. But now he wishes in vain to build a dam when the water has run down.