Valmiki Ramayana Ayodhya Kanda Sarga 5 Shloka 2
Original Shlokaगच्छोपवासं काकुत्स्थं कारयाद्य तपोधन। श्रीयशोराज्यलाभाय वध्वा सह यतव्रतम्।।2.5.2।।
1 source checked for this shloka
तपोधन O sage whose wealth is asceticism, गच्छ go, अद्य today, यतव्रतम् strictly observing vows, काकुत्स्थम् son of the family of Kakutstha (Rama), श्रीयशोराज्यलाभाय for securing prosperity, fame and kingdom, वध्वा सह along with my daughterinlaw, उपवासम् कारय advise him to undertake fast.
Could you, O sage, whose wealth is asceticism go to Rama engaged in strict observance of vows and advise him along with Sita, my daughterinlaw to undertake fast for securing prosperity, fame and kingdom.