What is the ruling on swearing falsely—unintentionally—to avoid lending money?

Deliberate lying is forbidden (haram), and swearing an oath upon it is even more forbidden (haram), constituting a "Ghamus oath" (a false oath taken intentionally). Its obligation is sincere repentance. The majority of scholars hold that its expiation is repentance and seeking forgiveness. The Shafi'is, however, believe that expiation for an oath is obligatory in addition to repentance.

If the oath was taken intentionally, then you must repent, and it is more cautious to offer expiation for the oath.

However, if the oath was uttered unintentionally, it falls under "laghw al-yamin" (a vain or idle oath) for which there is no blame, as Allah Almighty says: (Allah will not impose blame upon you for what is unintentional in your oaths).

Lying can be avoided through "tawriyah" (equivocation or dissimulation), based on the statement of 'Umar, may Allah be pleased with him: "Verily, in equivocation there is enough to spare a Muslim from lying."