Musannaf Ibn Abi Shayba 13:1502

Abu Bakr narrated to us, he said: Ibn Abi Za’idah narrated to us, from Ash’ath, from Ibn Sirin, who said: Do not stipulate any condition upon the *mudarib* (the entrepreneur in a profit-sharing partnership), for I fear that he may violate it, and thus corrupt [the contract] for you and for himself.