The doa for breaking fast is: 'Dhahaba al-dhama'u wabtallatil-'uruqu wa thabatal-ajru in sha Allah' — The thirst has gone, the veins have been moistened, and the reward is confirmed if Allah wills. This is recited at the moment of breaking the fast at Maghrib time.
ذَهَبَ الظَّمَأُ وَابْتَلَّتِ الْعُرُوقُ وَثَبَتَ الْأَجْرُ إِنْ شَاءَ اللَّهُ
Dhahaba al-dhama'u wabtallatil-'uruqu wa thabatal-ajru in sha Allah.
Meaning: The thirst has gone, the veins have been moistened, and the reward is confirmed, if Allah wills.
Source: Sunan Abu Dawud #2357The moment of breaking the fast is one of the times when doa is most accepted. Nabi (shallallahu alaihi wa sallam) said: 'Three doa-doa are not rejected: the doa of a fasting person at the time of breaking the fast, the doa of a just ruler, and the doa of the oppressed.' (Sunan al-Tirmidhi 3598)
ذَهَبَ الظَّمَأُ وَابْتَلَّتِ الْعُرُوقُ وَثَبَتَ الْأَجْرُ إِنْ شَاءَ اللَّهُ
When the Prophet (peace be upon him) broke his fast, he would say: 'Dhahaba al-dhama'u wabtallatil-'uruqu wa thabatal-ajru in sha Allah.'