פירוש על קידושין 39:2

Having used the word “for a slave” to teach that a father may not stipulate that his daughter not be designated, R. Meir needs a source for allowing the father to designate her to those unfit for her. This is a halakhah agreed to by all. To do this, R. Meir can use the verse that R. Eliezer used, “if she is found not pleasing to her master [so that he has not designated her].” And when it comes to relatives, he can agree with the sages that the father may not sell her to relatives.