Valmiki Ramayana Ayodhya Kanda Sarga 3 Shloka 40
Original Shlokaयतस्त्वया प्रजाश्चेमा स्स्वगुणैरनुरञ्जिताः।।2.3.40।। तस्मात्त्वं पुष्ययोगेन यौवराज्यमवाप्नुहि।
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यतः since, त्वया by you, इमाः these, प्रजाः people, स्वगुणैः with your virtues, अनुरञ्जिताः have been endeared, तस्मात् therefore, त्वम् you, पुष्ययोगेन when Pushya star is in conjunction with the Moon, यौवराज्यम् office of heirapparent, अवाप्नुहि receive.
As you have endeared yourself to these subjects with your virtues, you shall assume the office of heirapparent when Pushya star is in conjunction with the Moon.