“And if anyone gives a cup of cold water to one of these little ones because he is my disciple, I tell you the truth, he will certainly not lose his reward.”
This is from Matthew’s Gospel (NIV), and I do not believe that by “little ones” Jesus meant believing children (merely). He meant believers period.
A person who provides a follower of Christ with a cup of water will not lose his Heaven-sent reward, whatever it may be. But if he’s unsaved, what does it matter that he will get a reward if after he dies he just goes to Hell? How much value can the reward have?