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 wine, he would first mix water into it and then sell it. One day, the monkey grabbed his money pouch and climbed up a tree. The monkey began throwing one dinar into the sea and another into his master'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.)