Musannaf Ibn Abi Shayba 13:1486

Abu Bakr narrated to us, he said: Ibn Abi Za'idah narrated to us, from Muhammad ibn 'Amr, from Abu Salamah, from Abu Hurayrah, who said: The Messenger of Allah (may Allah bless him and grant him peace) said: "Do not meet the riders (traveling merchants) for the purpose of trade."