Dua for OPENING THE FAST/ romper el ayuno

ذَهَـبَ الظَّمَـأُ، وَابْتَلَّـتِ العُـروق، وَثَبَـتَ الأجْـرُ إِنْ شـاءَ الله

Thahabadh-dhama'u wabtallatil-'urooqu, wa thabatal-'ajru 'inshaa'Allaah.

The thirst is gone, the veins are moistened and the reward is confirmed, if Allah wills.
Abu Dawud 2/306 and others.