Hadith 826

وَقَالَ رَسُولُ اللَّهِ صَلَّى اللهُ عَلَيْهِ وَسَلَّمَ: " ثَلَاثٌ لَا يُرَدُّ لَهُمْ دَعْوَةٌ: الصَّائِمُ حَتَّى يُفْطِرَ، وَإِمَامٌ عَادِلٌ، وَدَعْوَةُ الْمَظْلُومِ يَرْفَعُهَا اللَّهُ فَوْقَ الْغَمَامِ وَيَفْتَحُ لَهَا أَبْوَابَ السَّمَوَاتِ، فَيَقُولُ الرَّبُّ: وَعِزَّتِي لَأَنْصُرَنَّكِ بَعْدَ حِينٍ ".
And the Messenger of Allah, peace and blessings be upon him, said: "There are three types of people whose supplication is not rejected: the fasting person until he breaks his fast, the just ruler, and the supplication of the oppressed. Allah raises it above the clouds, and the gates of the heavens are opened for it. Then the Lord, Blessed and Exalted, says: By My Honor! I will surely help you, even if after some time."
Hadith Reference مسند اسحاق بن راهويه / كتاب الدعوات / 826
Hadith Takhrij «سلسلة الضعيفة ، رقم : 1358 . ضعيف ترغيب وترهيب ، رقم : 1349 ، 1317 .»