This Du'a is taught by Imam Sajjad (as) and is Du'a #31 in Saheefa as sajjadiyyah. The du'a is a touching plea by one who acknowledges the enormity of the sins he has committed. His hope lies only in the mercy and forgiveness of Allah.
Using Qur'anic concepts of repentance, and its acceptance, Imam teaches us how to be sincere in seeking it. The Du'a reiterates the conditions of repentance, the physical signs present on a true repenter, and the legitimate hopes given to one who truly seeks forgiveness. It is a beautifully elegant way of expressing the remorse and hope of a faithful believer who has sinned.
“There is nothing more beloved to Allah than a believer who is repentant, male or female.” - Holy Prophet (saawa)