Valmiki Ramayana Bala Kanda Sarga 71 Shloka 21

वीर्यशुल्काम् as reward for prowess, सुरसुतोपमाम् equal to the daughter of devatas, मम सुताम् my daughter, सीताम् Sita, द्वितीयाम् second daughter, ऊर्मिलां चैव Urmila also, त्रि: three times, ददामि bestowing, संशय: न no doubt.

I offer my daughter Sita, who looks like a celestial maiden as reward for (Rama's) prowess and my second daughter Urmila (to Lakshmana). I proclaim it three times so that there is no doubt about it.