四分律比丘含注戒本 1.508

1.508

佛在羅閱祇。時，跋難陀往市肆上，以錢易錢。居士譏嫌，言「善能賣買」。比丘聞告，佛訶制戒。

The Buddha was in Rājagṛha. At that time, Upananda went to a market stall and exchanged coins for coins. Householders criticized him, saying, 'He is very skilled at buying and selling.' Bhikṣus heard this and reported it; the Buddha rebuked them and laid down the precept.