Sahih Bukhari Volume 008, Book 075, Hadith Number 364.

Narated By Abu 'Aqil : That his grandfather 'Abdullah bin Hisham used to take him from the market or to the market (the narrator is in doubt) and used to buy grain and when Ibn Az-Zubair and Ibn 'Umar met him, they would say to him, "Let us be your partners (in trading) as the Prophet invoked for Allah's blessing upon you." He would then take them as partners and he would Sometimes gain a whole load carried by an animal which he would send home.