Allahumma Rabba Shahr Ramadhan اللّهُمّ رَبّ شَهْرِ رَمَضَانَ 

Al-Kaf'amiy, in al-Balad al-Amin and al-Misbah has quoted the Kitab al-Ikhtiyar of Sayyid ibn Baqi that if one recites the following supplication everyday in Ramazan, Allah (swt) will forgive the sins of forty years of his age