When Vegeta found Gohan on Namek, he told him:
. . . Too bad, because you see, we are the last of the Saiyans, that means we have to look out for one another, understand? It's like... like the three of us are brothers...
Then, Vegeta kicks Gohan in the stomach. At that moment he had a big grudge against Goku and could've easily killed Gohan out of anger. Instead, the kick that he gave him was nonlethal.
Now I am wondering if there was some truth in Vegeta's words. As he already explained many times, the more of a beating a Sayian takes the stronger that Sayian becomes. Did he really want to help Gohan become stronger by kicking him?