The 231st prohibition is that we are forbidden from not lending money to one another with the intention of avoiding its release in the shemittah year.

The Torah prohibited us from having this concern in the verse,1 "Be very careful lest you...[say to yourself, 'the seventh year is approaching, and it will be the shemittah year.']"

The Sifri says: "The expressions 'hishomer' ("be very careful") and 'pen yi'hiyeh' ("lest") indicate prohibitions." This means that the usage of both expressions regarding this mitzvah gives added emphasis.