Valmiki Ramayana Ayodhya Kanda Sarga 109 Shloka 29
Original Shlokaशतं क्रतूनामाहृत्य देवराट् त्रिदिवं गतः। तपांस्युग्राणि चास्थाय दिवं याता महर्षयः।।2.109.29।।
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देवराट् king of the gods (Indra), क्रतूनाम् sacrifices, शतम् hundred, अहृत्य having performed, त्रिदिवम् to heaven, गतः went, महर्षयः great sages, उग्राणि intenese, तपांसि mortifications, आस्थाय after resorting to, दिवम् heaven, याताः attained.
After performing a hundred sacrifices, king of the gods (Indra) obtained (dominion over) heaven. Great sages attained heaven after resorting to intense mortifications.