Salam,
We are punished and rewarded in this world, but the purpose of this world is not to reward or punish. The punishments and rewards in this world are only to test us. The punishments are there to test our patience, and the rewards are to test our taqwa. The reward or punishment is not an end to itself(in this world) but only a means to something else, i.e. the test.
If you think about it (and there are many hadith and ayats in Quran on this same subject)...
The reward you have in this world are ephemeral. They last for a very short time, change from one moment to the next, and could be ended at any second by your own death, the death of someone else, or any other type of misfortune.
The same is true of the punishments.
If you think about someone like Saddam(la) who murdered and tortured millions of innocent men, women, and children and at the end of his life what happened. He hung on the end of a rope for a minute or so before he stopped breathing and then the ceasing of brain activity a minute or so after that (clinical death). So if you think about it in terms of this world, his crimes were many and far reaching and his punishment was very, very short and in no way commensurate with his crimes. So he didn't get his punishment in this world, the purpose of this world was to test him and he failed the test in a miserable and spectacular way. His punishment will be in the next life and whatever punishment he suffered here is inconsequential.
Also, you look at someone like the Prophet(p.b.u.h) or Imam Ali(a.s) or even someone like a marjaa taqleed or a shaheed. They spend their whole life in miserable conditions suffering all sorts of hardships and deprevations, constantly disappointed by those around them and constantly being betrayed by those close to them. At the same time, despite all this, they continue to exert the maximum effort in the
way of Allah(s.w.a). Obviously they passed the test, and whatever reward they received in this life is inconsequential compared to what Allah(s.w.a) has promised them in the next life.
These are obvious cases, but all of us will gravitate toward one of those polls and we will either pass or fail the test and then receive the compensation. InShahAllah, all of us will pass.
Also there is a hadith by Imam Hassan(a.s) about this subject.
A man came to Imam Hassan while he was walking thru the streets of Medina.
This man said to Imam Hassan, 'You say that this world is a paradise for the unbelievers and a prison for the believers'.
Imam Hassan said, 'Yes, I said that'
So the man continued, 'Well I am an unbeliever (kafir). Yet, I suffer a great deal in this world. The sun has weakened my body, my children have abandoned me, and I am suffering all kinds of illness. So how is it that this world is a Paradise for me, while I see you eating nice food, in a good house, surrounded by friends and family, and with a healthy body, and yet you are a believer and I am an unbeliever. '
Imam Hassan told him. 'The suffering you are experience is nothing compared to what you will suffer (If you die as a kafir. You will look back on this life, and it will seem to you as a wide garden. At the same time, the benefits I am experiencing in this life are nothing compared to what Allah(s.w.a) has promised the believers in the next world. The believer will look back on this world (from the garden) and consider it to be a very miserable prison, even if in this world he had great wealth.'
Edited by Abu Hadi, 29 August 2012 - 08:29 PM.
Hadith #32.
With my continuous chain of transmission reaching up to Muhammad ibn Ya'qub al-Kulaynl, from al-Husayn ibn Muhammad, from al-Mu'alla ibn Muhammad, from al-Hasan ibn 'All al-Washsha', from 'Abd Allah ibn Sinan, from Abu 'Abd Allah, may Peace be upon him, which he said:
"Among the things pertaining to the soundness of a Muslim's certitude [in faith] is that he would not please people while displeasing God, nor blame them for something that God has not given him. For, verily, [God's] rizq (provision, sustenance) is not brought about by anybody's greed, nor is it withheld by anyone's disapproval, and were anyone of you to flee from his rizq like he flees death, his rizq would overtake him in the way he is overtaken by death." Then he added, "Indeed Allah with His justice and fairness, has put joy and comfort in certainty (yaqin) and satisfaction (al- rida) and He has put sorrow and grief in doubt and dissatisfaction."
http://www.al-islam.org/40hadith/