عَنِ ابْنِ عَبَّاسٍ رَضِیَ اللہُ عَنْہُ أَنَّ رَسُوْلَ اللہِ صَلَّی اللہُ عَلَیْہِ وَسَلَّمَ بَعَثَ مُعَاذَ بْنَ جَبَلٍ اِلَی الْیَمَنِ فَقَالَ اتَّقِ دَعْوَۃَ الْمَظْلُوْمِ فَاِنَّھَا لَیْسَ بَیْنَھَا وَبَیْنَ اللہِ حِجَابٌ
Hazrat Ibn Abbasra narrated, “The Holy Prophet, peace and blessings of Allah be upon him, sent Muaz bin Jabal to Yemen, and said, ‘Beware of the supplication of the oppressed, for indeed, there is no barrier between it and Allah.’”
(Jami‘ al-Tirmidhi, Kitab al-Bir wa al-Sila an Rasool Allah)