Mambo Ya Walawi 20:12

“ ‘Ikiwa mtu atakutana kimwili na mke wa mwanawe, lazima wote wawili wauawe. Walichokifanya ni upotovu; damu yao itakuwa juu ya vichwa vyao wenyewe.

And if a man lie with his daughter in law, both of them shall surely be put to death: they have wrought confusion; their blood shall be upon them.