It is narrated from Sayyiduna Mu'awiyah (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "A nation is not deemed pure in which judgement is not given according to the truth, and in which the weak cannot take his right from the strong without hindrance."
Hadith Referenceالمعجم الكبير للطبراني / باب الميم / 16952