The 162nd prohibition is that the Kohen gadol is forbidden from having relations with a widow, even without marriage.
The source of this commandment is G‑d's statement,1 "he will then not profane his children."
The explanation of this is that a regular Kohen is prohibited from marrying [a divorcee, chalalah, or zonah], as it is written,2 "they shall not marry," meaning kiddushin. Nevertheless, he does not receive lashes unless he has relations with her, as explained above.3 If, however, he had relations with her without marriage — although it is prohibited and he invalidates her [i.e. makes her a chalalah] — he does not receive lashes, since it is not explicitly mentioned.
Regarding a Kohen gadol, though, there are two distinct prohibitions: one being "he must not marry," i.e. the prohibition of marriage; and the second, "he will then not profane his children," i.e. having relations even without marriage.
Tractate Kiddushin says,4 "Rava agrees regarding a Kohen gadol and a widow — that if he has relations without marrying her, he receives lashes. [The reason is that] the verse says, 'he will then not profane his children,' but he did."
It also says there, "a Kohen gadol [who marries and has relations] with a widow receives two sets of lashes: one for 'he must not marry,' and one for, 'he will then not profane his children.' "
This prohibition applies exclusively to [relations with] a widow,5 because she is the only one prohibited to the Kohen gadol and permitted to a regular Kohen. Therefore, with this act of relations she first became a chalalah and prohibited to a regular Kohen.
Regarding [a Kohen gadol with] a divorcee, zonah, or chalalah, however, the law is just like that of a regular Kohen [and he does not receive lashes for having relations if there was no marriage]. This is because they were all invalid for a regular Kohen to begin with, and were only repeated regarding a Kohen gadol for the reason mentioned above.6
