Since the slave's son was not sold, why does it say "Hu u'Banav Imo"?
Rashi: From the Pasuk we can extrapolate that throughout the term of the Eved Ivri, the master is obligated to feed his children 1 , and when his contract ends, this obligation falls away.
What is the Pasuk mean when it writes "v'El Achuzas Avosav Yashuv"?
Rashi: This means that the Eved Ivri regains his original status, and one is not permitted to taunt him (because he was an Eved).
Moshav Zekenim citing Ri: This is the source that a Nirtza returns in Yovel. Rashi (10) expounded this from "v'Ish El Mishpachto."