Musannaf Ibn Abi Shayba 35:203

Ibn Abi Za'idah narrated to us, from Ubaydullah, from Nafi', from Ibn Umar, who said: The Prophet (peace be upon him) forbade *al-talaqqi* (meeting the caravans outside the market to buy their goods before they reach the market). And he mentioned that Abu Hanifah said: There is no harm in it.