פירוש על קידושין 118:18

If Rav agrees with the Sages who referred to the case of divorce, why not just say “the halakhah agrees with the Sages.” The Talmud explains that Rav needs to teach his statement in relation to betrothal for had he not we might have thought that when it comes to betrothal, the Sages would agree with Shmuel that it is a stipulation. Since betrothal is to draw her near, we might assume that he is not retracting his statement.