It is narrated from Sayyiduna Abu Hurayrah (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) said: "There are three kinds of people whose supplication Allah does not reject: (1) the just ruler, (2) the fasting person until he breaks his fast, and (3) the supplication of the oppressed; it is carried upon the clouds, the gates of heaven are opened for it, and Allah, the Lord of Might, says: By My might, I will surely help it, even if after a while."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب آداب القاضي / 20163