Negative Commandment #138
Sefer Ha’mitzvos Ha’Katzar (The concise book of mitzvos)
By the Chofetz Chaim
This book lists the Torah mitzvos that can be observed today
Second Section – the Negative Commandments
138. It is a negative commandment "a Cohain may not marry a woman is a Zonah"
As it states in Vayikra (Leviticus) 21:7, "a woman who is a Zonah... they shall not take." According to Torah law, a Zonah is a woman who is either not the daughter of a Jew or a Jewish woman that has relations with a man who she is forbidden to marry or a woman who had relations with an illegitimate Cohain (even though she was allowed to marry him). She is a Zonah even if she was forced to have relations or had them in an unnatural way. But if a single woman made herself available to all for payment, or if he had relations with a ritually impure woman, or she had relations with an animal, she is not considered a Zonah in this case.
This applies in all places and at all times.