The 358th prohibition is that a rapist is forbidden from divorcing the woman he raped.1
The source of this commandment is G‑d's statement,2 "He must then take her to be his wife, and he may not send her away as long as he lives."
This prohibition is preceded by the positive commandment,3 "He must then take her as his wife." In tractate Makkos4 it is clearly explained that this is considered a "prohibition which is preceded by a positive commandment."
It is also said there, "A rapist who divorces his wife — if he is not a Cohen, he remarries her and does not receive lashes. If he is a Cohen, he receives lashes, and he may not remarry her [since a Cohen may not marry a divorcee]."5
You should keep in mind that even a non-Cohen will receive lashes for divorcing the woman he raped, if he cannot perform the remedial positive command [of remarrying her]. This would be in a case where she died before he remarried her, or she married another man after he divorced her.6 This corresponds to our principle, "If he fulfilled [the remedial positive commandment, he does not get lashes]; if he did not fulfill" [this commandment, he would receive lashes].7
The details of this mitzvah are explained in the third and fourth chapters of Kesubos.
