Ibn al-Hanba’ reported: Ali, may Allah be pleased with him, said, “Three supplications are never turned away: a just leader for his subjects, a parent over his child, and the supplication of the oppressed.”
Source: Musnad ibn al-Jaʻd 2401
عَنِ ابْنِ الْحَبْنَاءِ التَّمِيمِيِّ عَنْ عَلِيٍّ رضي الله عنه قَالَ ثَلَاثَةٌ لَا تُرَدُّ دَعْوَتَهُمُ الْإِمَامُ الْعَادِلُ عَلَى رَعِيَّتِهِ وَالْوَالِدُ عَلَى وَلَدِهِ وَدَعْوَةُ الْمَظْلُومِ
2401 مسند ابن الجعد