Commentary for Kiddushin 45:5

אי הכי אימא סיפא בשטר על ידי עצמו על ידי עצמו אין על ידי אחרים לא ואי מדעתו על ידי אחרים אמאי לא

and we learned: One may obtain a privilege for a person in his absence, but cannot so act to his disadvantage.<span class="x" onmousemove="('comment',' Such an action being invalid.');">⁵</span> Hence it obviously means with his knowledge [consent], and we are informed this: only through the agency of others [can he be emancipated thus,] but not through his own, thus proving that a slave has no rights of acquisition apart from his master.<span class="x" onmousemove="('comment',' As explained in the note on the Mishnah, q.v.');">⁶</span>

Daf Shevui to Kiddushin