Responsa sobre I Reyes 3:33

They responded: "It shall be neither yours nor mine; cut it in two!" (I Kings 3:26), and within the vision they explained that it shall follow neither the stringent ones nor the lenient. Rather, the time between the setting of the sun and the appearance of the stars should be divided in two, and this point is the midpoint of twilight referred to by Rabbi Yehuda⁵cf. Shabbat 34b:3.