Commentary for Kiddushin 99:4
אלא אמר רב יוסף מהכא המקדש את האשה ואמר כסבור הייתי שהיא כהנת והרי היא לויה לויה ונמצאת כהנת ענייה והרי היא עשירה עשירה והרי היא ענייה מקודשת מפני שלא הטעתו ואמאי הא קאמר כסבור הייתי אלא משום דאמרינן דברים שבלב אינן דברים אמר ליה אביי דלמא שאני התם דלחומרא
But [it follows] from the second clause: and you find it likewise in the case of women's divorce and slaves' manumission: he [the husband or master] is compelled, until he declares,'I am willing.'<span class="x" onmousemove="('comment',' This refers to those who are compelled to free their wives or slaves.');"><sup>4</sup></span> Yet why: seeing that in his heart he is unwilling! Hence it must surely be because we say: A mental declaration is not recognised! - But perhaps it is different there, because it is a religious duty to obey the words of the Sages! - But, said R'Joseph, [it is deduced] from the following: If one betroths a woman and [then] declares, 'I thought her to be a priest's daughter, whereas she is the daughter of a Levite,' or 'a Levite's daughter and she is the daughter of a priest'; 'is poor, whereas she is wealthy', or 'is wealthy whereas she is poor' 'she is betrothed, because she has not deceived him.