Sayyiduna Abu Mas'ud (may Allah be pleased with him) said: A man asked the Prophet (peace and blessings be upon him): O Messenger of Allah (peace and blessings be upon him)! How can I know whether I have done well or badly? He (peace and blessings be upon him) said: "Listen to your neighbour: if he says that you have done well, then it is good; and when you hear them saying: You have done badly, then you have indeed done badly."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب آداب القاضي / 20396