مَنْ فَطَّرَ صَائِمًا كَانَ لَهُ مِثْلُ أَجْرِهِ غَيْرَ أَنَّهُ لَا يَنْقُصُ مِنْ أَجْرِ الصَّائِمِ شَيْئًا
Man fattara sa'iman kana lahu mithlu ajrihi ghayra annahu la yanqusu min ajris-sa'imi shay'a
Whoever provides iftar to a fasting person will have the same reward as him, without diminishing anything from the fasting person's reward.
While this is a hadith rather than a du'a, it is a powerful reminder during Ramadan. Even providing a single date or glass of water to someone breaking their fast earns you the full reward of their entire day of fasting.
Related Du'as
اللَّهُمَّ أَعِنِّي عَلَى صِيَامِهِ وَقِيَامِهِ
O Allah, help me to fast and pray during it (Ramadan).
Atharذَهَبَ الظَّمَأُ وَابْتَلَّتِ الْعُرُوقُ وَثَبَتَ الْأَجْرُ إِنْ شَاءَ اللَّهُ
The thirst is gone, the veins are moistened, and the reward is confirmed, if Allah wills.
Hasanاللَّهُمَّ أَهِلَّهُ عَلَيْنَا بِالْأَمْنِ وَالْإِيمَانِ وَالسَّلَامَةِ وَالْإِسْلَامِ رَبِّي وَرَبُّكَ اللَّهُ
O Allah, let this moon rise upon us with security, faith, safety, and Islam. My Lord and your Lord is Allah.
Hasanاللَّهُمَّ بَلِّغْنَا رَمَضَانَ وَأَعِنَّا عَلَى صِيَامِهِ وَقِيَامِهِ وَتَقَبَّلْهُ مِنَّا
O Allah, let us reach Ramadan, help us to fast and pray in it, and accept it from us.
Hasan