四分律比丘含注戒本 1.520

1.520

Bhikṣuṇīs commit the same offence. As for cases where there is no offence: the five assemblies of renunciants are permitted to exchange among themselves; they should assess and settle it themselves, not raising and lowering [prices] as in the manner of the marketplace; one must not trade with other people. One may cause a lay attendant (kappiya-kāraka) to trade. If one regrets [the transaction], it is permitted to return [the goods]. If ghee and oil are exchanged for one another, there is no offence.