Kulthum al-Khuza'i (may Allah be pleased with him) said: A man came to the Prophet (peace and blessings be upon him) and said: O Messenger of Allah! If I do good or bad, how can I recognise it? He (peace and blessings be upon him) said: "When your neighbours say that you have done good or bad, then you truly have done good or bad."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب آداب القاضي / 20397