Complex sentence: The Talmud (Kiddushin 68b) derives this law from the Torah, specifically from Deuteronomy 7:3-4, which reads: Thy daughter thou shalt not give to his son, nor shalt thou take his daughter to thy son.
Split into simpler sentences: The Talmud (Kiddushin 68b) derives this law from the Torah. The relevant Torah passage (Deut.7:3-4) reads: Thy daughter thou shalt not give to his son, nor shalt thou take his daughter to thy son.