Sayyiduna Jabir bin Abdullah (may Allah be pleased with them both) says that the Messenger of Allah (peace and blessings be upon him) forbade "al-muzabanah (muzabanah) and al-muhaqalah (muhaqalah), and al-thunya (an exception) as well, but if it is known, then it is permissible."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب البيوع / 10621