פירוש על קידושין 46:8

According to Rabbah, in general everyone holds that anything a slave acquires, his master automatically acquires as well. The dispute in the mishnah is only in a case where someone gives the slave money on condition that the master not have any rights to it. R. Meir says that this condition does not work, whereas the rabbis hold that it does. Therefore, R. Meir holds that there is no way for the slave to buy his own freedom, whereas the rabbis would hold that as long as others gave him the money and said, “on condition that your master has no right to it,” the slave may use that money to free himself.