Sefer HaChinuch, Mitzvah 63

[Mitzvah 63] is not to oppress converts verbally. We have been prevented from oppressing converts, even verbally, as it says: "and you shall not oppress a convert." The Torah added an additional warning as it says: "do not oppress" another time. Because the issue of oppression is more relevant to a convert than it is to other Jews, as most other Jews have (Jewish) relatives who will redress their grievances. And there is another reason, [that is] because there is a concern that [the convert] might leave the fold out of anger over abuse. And they said in the (Midrash) Sifra that one shouldn't say, "Yesterday you were an idolater and today you are entering under the wings of the Divine Presence?" Among the roots of the mitzvah, aside from what we've already written, in order to permanently train our negative inclination not to do whatever evil is in our power to do. Therefore we are warned regarding this person who is among us without [a full support system] and whom everyone can exert some power over, that we not exclude him from the general [sensitivity that we show to everyone among us]. And through boundaries such as these we will acquire a soul of higher worth, raised-up and crowned with (positive) characteristics, worthy of receiving good. And we will perfect in ourselves the desire of the Blessed One who desires to give benefit... ...[This law] applies in all places and at all times, to men and to women. [translation by AJWS]