Halakhah for Sanhedrin 149:21

I have also seen about the matter of this commandment in the books of my teacher, may God protect him, that any woman for which betrothal (kiddushin) is effective - such as a widow to a high priest, a divorcee or released woman to a common priest, a mamzeret or a netinah to an Israelite and an Israelitess to a mamzer - are not included in the sexual prohibitions, for which one must die. Still, we nonetheless do not instruct any man to have intercourse with any woman - even if she is single, we do not instruct [it]. He should instead die from the illness that has come from his lust and not have her have intercourse with him or [even] speak with her, etc. - [as we see] in Sanhedrin 75a and the Book of Knowledge (Mishneh Torah, Foundations of the Torah 5:9). And the rest of its details are elucidated in Chapter 8 of Sanhedrin and in Pesachim and Yoma and in other places (see Tur, Yoreh Deah 157).