Sayyiduna Abu Hurayrah (may Allah be pleased with him) says: "Two sales have been forbidden, namely al-mulamasah and al-munabadhah. Al-mulamasah is that each of the two touches his companion's garment without looking at it, and al-munabadhah is that each of them throws his garment to the other and neither of them even looks at the other's garment."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب البيوع / 10867