Beware of the invocations of the oppressed person, for, indeed, they rise to heaven as if they were sparks of fire
Authentic hadithعن ابن عمر رضي الله عنهما مرفوعاً: «اتَّقُوا دَعَوَاتِ المظلومِ؛ فإنَّها تصعد إلى السماء كأنَّها شَرارٌ».
Ibn ‘Umar (may Allah be pleased with him) reported that the Prophet (may Allah's peace and blessings be upon him) said: "Beware of the invocations of the oppressed person, for, indeed, they rise to heaven as if they were sparks of fire."
Explanation
Avoid oppression, and fear the supplication of the oppressed one, for it ascends to Allah in the heavens as if it is a spark of fire. It was compared to a spark in the swiftness of its rise in the sky, or because it comes out of a heart that is burning with the fire of injustice and suffering, and it is like the spark in the way it penetrates the heavenly barriers.
Source · Al-Haakim
From the Hadith Encyclopedia (hadeethenc.com).