Habib bin Ubayd narrates: Sayyiduna al-Miqdam bin Ma'dikarib (may Allah be pleased with him) had a slave girl who used to sell milk, and Sayyiduna al-Miqdam (may Allah be pleased with him) would collect the price himself. It was said to him about this: "Subhan Allah! She sells the milk and you keep the price?" He said: "Yes! There is no harm in it. I heard the Prophet (peace and blessings be upon him) say: 'A time will certainly come upon people in which nothing will benefit except the dinar and the dirham.'"
Imam Ahmad recorded it in this way.
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب البيوع / 6243