For a man not to have intercourse with his daughter-in-law (his son’s wife), even after she is no longer married to his son (if she is still married, she is prohibited by death penalty under
commandment -347). This rule was not binding on gentiles under the original Seven Noahide Laws, but in ancient times the human race voluntarily adopted the stricter prohibitions on marital relations as found in Jewish Law, and this and similar restrictions have applied to all gentiles ever since.