Ali bin Rabi'ah al-Walibi (may Allah have mercy on him) said: I asked Sayyiduna Ibn Umar (may Allah be pleased with them both) about al-ma'un, and he said: "What do people say about it?" I said: "They say it is what people take and give among one another." He said: "They are saying nothing (correct); it is wealth whose due is not given."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الزكاة / 7797