Musnad Ahmad

It is narrated from Hazrat Abu Huraira (may Allah be pleased with him) that the Noble Prophet (peace and blessings be upon him) said: A man, in connection with trade, boarded a boat carrying wine. There was also a monkey with him. Whenever the man sold the wine, he would first mix water into it and then sell it. One day, the monkey grabbed his purse of money and climbed up a tree. The monkey began throwing one dinar into the sea and another into his owner's boat, until he had divided them equally. (From here, the saying became famous: the milk was separated from the water, and the water from the milk.)