Is it permissible to retract an oath made contingent on a forbidden act without specifying a time, and is expiation (kaffarah) required in this case, and what are the implications for the oath if the intention is broken?

Such an oath is binding and necessitates expiation (kaffarah) upon breaking it. If one breaks it once, the oath is dissolved, and one is not required to repeat the expiation if the breaking is repeated. This is the general rule, unless the oath inherently implies repetition through its wording, the intention of the one who swore it, or by custom.