I've never heard anyone use the prophets reward in any lesson on giving before. It is a new angle. While I agree with Toolite above ^^ But, may I add,there is a darker side to a prophets reward; That is that people like to kill prophets because they don't want to hear what they have to say. In other words a prophet can get killed for doing the very thing that God wanted them to do. In that case a prophets reward is in heaven (a place that, by doing the very thing that God asked of them, they may go to sooner then they anticipated).
Even if a prophet is not killed for saying and doing what God wanted them to do, they can be ignored, ridiculed and considered of little value. Sometimes I wonder if this a fate worse then death for them. Imagine burning with very words of God and delivering that message in the very way that God told them to only to have the recipients of this word give little more then a bronx cheer in response. Imagine seeing with such clarity the consequences of the sin that a person or a group of people are doing only to be called stupid, short sighted, worthless and of little consequence. What kind of reward is that?
In the same way don't be disapointed when the very people you care about and so dilligently fast and pray for do not want what you are doing for. In the same way don't expect the people who you are giving your time or money to to be appreciative of either. Time and time again I have given the best financial offering that I could afford to the church only to have it looked upon as an igsignifigant pittance, whilst others, who did not give anywhere near their best, were honored. Size matters, it's just that God has a different measuring stick. He measures by how much selfless generosity and humans measure by dollar ammount.
Depressed yet? Don't be. It's better to suffer the consequences of doing God's will then suffer the often unseen consquences of not doing God's will. I believe reward will come, but you may have to wait untill you get to heaven before you recieve it. Man that still sounds like a downer. I can really stink at being cheery. Sorry.
s