The Holy Prophet (peace be upon him and his holy household) has said
that one who recites this supplication after each obligatory prayer in month of Ramadan will have all his sins forgiven up to the day of Resurrection:

Ref: Duas.org

In the name of Allah, the most Merciful, the most Beneficent	بِسْمِ ٱللَّهِ ٱلرَّحْمٰنِ ٱلرَّحِيمِ
O Allah, instil happiness in the inhabitants of the graves	اللّهُمَّ أَدْخِلْ عَلَى أَهْلِ الْقُبُورِ السُّرُورَ
O Allah, enrich every poor person	اللّهُمَّ أَغْنِ كُلَّ فَقِيرٍ
O Allah, satisfy every hungry person	اللّهُمَّ أَشْبِعْ كُلَّ جَائِعٍ
O Allah, clothe every unclothed one	اللّهُمَّ اكْسُ كُلَّ عُرْيَانٍ
O Allah, facilitate the payment of every one in debt	اللّهُمَّ اقْضِ دَيْنَ كُلِّ مَدِينٍ
O Allah, provide relieve for every anguished one	اللّهُمَّ فَرِّجْ عَنْ كُلِّ مَكْرُوبٍ
O Allah, return every traveler to his home	اللّهُمَّ رُدَّ كُلَّ غَرِيبٍ
O Allah, free every captive	اللّهُمَّ فُكَّ كُلَّ أَسِيرٍ
O Allah, reform every corrupt affair of the Muslims	اللّهُمَّ أَصْلِحْ كُلَّ فَاسِدٍ مِنْ أُمُورِ الْمُسْلِمِينَ
O Allah, cure every sick person	اللّهُمَّ اشْفِ كُلَّ مَرِيضٍ
O Allah, relive our poverty with provisions from Your needlessness	اللّهُمَّ سُدَّ فَقْرَنَا بِغِنَاكَ
O Allah, change our unpleasant state into Your beautiful state	اللّهُمَّ غَيِّرْ سُوءَ حَالِنَا بِحُسْنِ حَالِكَ
O Allah, facilitate the payment of our debt and save us from poverty	اللّهُمَّ اقْضِ عَنَّا الدَّيْنَ وَأَغْنِنَا مِنَ الْفَقْرِ
For surely You are all-powerful over everything	إنَّكَ عَلَى كُلِّ شَيْءٍ قَدِيرٌ