Sayyiduna Anas (may Allah be pleased with him) said that the Messenger of Allah (peace and blessings be upon him) forbade "al-mukhadarah (selling fruit before it ripens), al-muhaqalah (a person selling a crop of wheat for a hundred faraq), and al-muzabanah (selling the dates on a palm tree for dried dates by a fixed measure, on the terms that if they turn out more it is my right and if less I am liable to make it up)." And Ibn Umar bin Yunus (may Allah have mercy on him) added: "al-munabadhah (a man throws his garment to another and the deal between them is settled without looking and without mutual consent) and al-mulamasah (a person touches another person's garment, whether by day or night, without turning it over to examine it)."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب البيوع / 10582