Sahih Bukhari Volume 003, Book 031, Hadith Number 213.

Narated By Abu Huraira : Two fasts and two kinds of sale are forbidden: fasting on the day of 'Id ul Fitr and 'Id-ul-Adha and the kinds of sale called Mulamasa and Munabadha. (These two kinds of sale used to be practiced in the days of Pre-lslamic period of ignorance; Mulamasa means when you touch something displayed for sale you have to buy it; Munabadha means when the seller throws something to you, you have to buy it.)