Withhold not good from them to whom it is due, when it is in the power of thine hand to do {it}. {them...: Heb. the owners thereof} Say not unto thy neighbour, Go, and come again, and to morrow I will give; when thou hast it by thee. Devise not evil against thy neighbour, seeing he dwelleth securely by thee. {Devise...: or, Practise no evil} Strive not with a man without cause, if he have done thee no harm.
Provérbios 3:27-30
Proverbs also brings a wise advice: do not devise evil against your neighbor. Unfortunately we have to live every day with people who plot evil against each other. In their thinking, they always want something good for you, even for this have to harm the other. Often we do not do any harm to them, but received as a reward to the evil you have done well.
The word of God condemns it: He that knoweth to do good and not do it, sins.
The next time you can help someone, do not tell him that he can not, do not tell him to return later. God is pleased when you do well even if you receive nothing in return, for your reward will be given by God himself.