Sahih Muslim Book 10, Hadith Number 3623.

Chapter : It is forbidden to meet the traders in the way for getting undue advantage.

Ibn ‘Umar (Allah be pleased with them) reported Allah’s Messenger (may peace be upon him) as saying: Do not go out to meet merchandise in the way, (wait)until it is brought into the market. This hadith has been reported on the authority of Ibn Numair but with a slight change of words.