194. The Arayos – Granddaughter II: The prohibition against relations with a daughter's daughter
…or your daughter’s daughter you shall not uncover. (Leviticus 18:10)
We can just re-read the previous mitzvah and substitute the word “daughter” wherever “son” appears.
This mitzvah applies in all times and places. In the Talmud, it is discussed in the tractates of Yevamos (22a, 97a) and Sanhedrin (75a). It is codified in the Shulchan Aruch in Even Ha’Ezer 15 and is #335 of the 365 negative mitzvos in the Rambam’s Sefer HaMitzvos. It is so completely identical to the previous mitzvah that the Chofetz Chaim combines them as #119 of the 194 negative mitzvos that can be fulfilled today in his Sefer HaMitzvos HaKatzar.