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 صَلِّ عَلَى مُحَمَّدٍ وَعَلَى آلِ مُحَمَّدٍ كَمَا صَلَّيْتَ عَلَى إِبْرَاهِيمَ وَعَلَى آلِ إِبْرَاهِيمَ إِنَّكَ حَمِيدٌ مَجِيدٌ
O Allah, send blessings upon Muhammad and the family of Muhammad, as You sent blessings upon Ibrahim and the family of Ibrahim. Indeed, You are Praiseworthy and Glorious.
Sahihاللَّهُمَّ سَلِّمْنِي لِرَمَضَانَ وَسَلِّمْ رَمَضَانَ لِي وَتَسَلَّمْهُ مِنِّي مُتَقَبَّلًا
O Allah, keep me safe for Ramadan, keep Ramadan safe for me, and accept it from me.
Hasanاللَّهُمَّ بَلِّغْنَا لَيْلَةَ الْقَدْرِ وَاجْعَلْنَا فِيهَا مِنَ الْمَقْبُولِينَ وَلَا تَحْرِمْنَا خَيْرَهَا وَاكْتُبْ لَنَا فِيهَا الْعِتْقَ مِنَ النَّارِ
O Allah, let us reach Laylatul Qadr, make us among the accepted in it, do not deprive us of its goodness, and decree for us in it freedom from the Fire.
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.
Hasan