Sunan Ibn Majah Book 7, Hadith 1752

حَدَّثَنَا عَلِيُّ بْنُ مُحَمَّدٍ، حَدَّثَنَا وَكِيعٌ، عَنْ سَعْدَانَ الْجُهَنِيِّ، عَنْ سَعْدٍ أَبِي مُجَاهِدٍ الطَّائِيِّ، - وَكَانَ ثِقَةً - عَنْ أَبِي مُدِلَّةَ، - وَكَانَ ثِقَةً - عَنْ أَبِي هُرَيْرَةَ، قَالَ قَالَ رَسُولُ اللَّهِ ـ صلى الله عليه وسلم ـ ‏ "‏ ثَلاَثَةٌ لاَ تُرَدُّ دَعْوَتُهُمُ الإِمَامُ الْعَادِلُ وَالصَّائِمُ حَتَّى يُفْطِرَ وَدَعْوَةُ الْمَظْلُومِ يَرْفَعُهَا اللَّهُ دُونَ الْغَمَامِ يَوْمَ الْقِيَامَةِ وَتُفْتَحُ لَهَا أَبْوَابُ السَّمَاءِ وَيَقُولُ بِعِزَّتِي لأَنْصُرَنَّكِ وَلَوْ بَعْدَ حِينٍ ‏"‏ ‏.‏

It was narrated from Abu Hurairah that the Messenger of Allah (ﷺ) said:There are three whose supplications are not turned back: A just ruler, and a fasting person until he breaks his fast. And, the supplication of one who has been wronged is raised by Allah up to the clouds on the Day of Resurrection, and the gates of heaven are opened for it, and Allah says, ‘By My Might I will help you (against the wrongdoer) even if it is after a while.’”