Valmiki Ramayana Aranya Kanda Sarga 66 Shloka 3
Original Shlokaमहता तपसा राम महता चापि कर्मणा। राज्ञा दशरथेनासि लब्धोऽमृतमिवामरैः।।3.66.3।।
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राम Rama, राज्ञा by the king, दशरथेन by Dasaratha, महता great, तपसा penance, महता great, कर्मणाचापि the action, अमरैः by the gods, अमृतमिव like nectar, लब्धः असि obtained.
O Rama king Dasaratha begot you by doing a great penance and performing great deeds, just as gods begot the nectar.