Musnad Ahmad 31:575

Abu Kamil narrated to us, Hammad narrated to us, from Hammad, from Ibrahim, from Abu Sa’id al-Khudri: "That the Prophet, may Allah bless him and grant him peace, forbade hiring a worker until his wage is clarified to him. And [he forbade] an-najash (bidding up the price without the intention to buy), al-lams (a form of pre-Islamic sale by touching), and ilqa’ al-hajar (a form of pre-Islamic sale by throwing a stone)."