Leviticus 20:14

And if a man take a wife, and her mother,.... Marry both the one and the other, or commit uncleanness with them, they consenting to it:

it [is] wickedness; abominable wickedness, shocking and detestable; there are other things, which also are wicked and not to be done, but this is extremely wicked, wickedness to a high degree:

they shall be burnt with fire, both he and they; the man, the mother and her daughter both being married together to him, or both consenting to his lying with them; otherwise, if one of them was first his wife, it was not reasonable that she should be put to death; and therefore some interpret "they", one of them, as Jarchi observes, one or other of them; and so Aben Ezra explains it, this or that; if the mother was his wife, the daughter was to be burnt; and so on the contrary, if the daughter was his wife, the mother was to be burnt; according to the Targum of Jonathan, they were to be burnt by pouring lead into their mouths: and so the manner of burning is described in the Misnah g; they that are to be burnt are fixed in dung up to their knees, then they put a hard napkin within a soft one, and roll it about is neck; one draws it one way, and another another way, until he opens his mouth; then they take hot melted lead, and pour it into his mouth, which goes down into his bowels and burns them. But it was rather done with faggots, of which an instance is given:

that there be no wickedness among you; of such kind, continued, countenanced, and pass unpunished. This punishment was to be inflicted, to deter persons from it. The law against it is in Leviticus 18:17.

g Sanhedrin, c. 7. sect. 2.