When an established presumption that people are close relatives has been established, we judge accordingly even though there is no clear proof that they were relatives. We give lashes and execute by burning, stoning, and strangulation based on such a presumption.
What is implied? If it is an accepted presumption that a particular woman is a man's sister, daughter, or mother and he had relations with her in the presence of witnesses, he is given lashes or executed by burning or stoning even though there is no clear-cut evidence that the woman is his sister, mother, or daughter, only the accepted presumption.
An incident occurred with a woman who came to Jerusalem carrying an infant on her shoulders and she raised it, [establishing] the assumption that he was her son. [After he grew older,] he had relations with her and they brought her to the court who executed her by stoning.
A proof of this law can be drawn from the fact that the Torah speaks of the judgment of execution for one who curses his father and strikes his father How can we find clear proof that he is his father? Instead, we operate according to the existing presumption. So, too, with regard to other relatives, we operate according to the existing presumption.