I don't think that it will be easy to find a specific quote of kindness in Wiesel's narrative because, frankly, there is not much in way of kindness to witness.  I would say that one particular instance where there is kindness spoken is in chapter 5.  The inheritance scene between Eliezer and his father is one where there is kindness.  The father, afraid of being selected, implores Eliezer to keep the knife and spoon that will serve as a type of "inheritance" and "remembrance" once the father is selected.  There is something about this moment, one shrouded in sadness and in pain, where there is kindness in how both the father begs the son to take the tokens of the family name, and how the son recognizes that it is his duty to honor his father.  In a setting like the Holocaust, the kindness that both bonds display in deferential honor to the other is significant.  There are not many moments like this in the narrative, and I would feel that this one would stand out as an instant of kindness and of caring.  Certainly, the quotes of how Eliezer's father tells him to take the knife and spoon and how the narrative describes Eliezer being obliged to take it, all the while trying to deny how the last connection to his family might be killed off, are reflective of the human kindness that prisoners of the Nazis showed to one another in their final moments.  It is a representation of kindness that one can only hope was replicated in different settings throughout the Holocaust.