Surya Siddhanta
तन्मद्ख्यसूत्रसम्योगाद् बिन्दुत्रिस्पृग् लिखेद् धनुः। प्राग्बिम्बम् यादृग् एव स्यात् तादृक् तत्र दिने शशी॥
From the point of intersection of the lines passing through their midst describe an arc touching the three points : as the disk already drawn appears, such is the moon upon that day.
english translation