But he who does of righteous deeds while he is a believer – he will neither fear injustice nor deprivation.
أخرج الطبري بسنده الحسن عن قتادة قوله (ومن يعمل من الصالحات وهو مؤمن) وإنما يقبل الله من العمل ما كان في إيمان
Qataadah said regarding this Verse that Allaah only accepts those deeds which are done in 'Imaan [i.e. when a person is a believer].
أخرج الطبري بسنده الحسن عن علي بن أبي طلحة عن ابن عباس قوله: (فلا يخاف ظلما ولا هضما) ، قال: لا يخاف ابن آدم يوم القيامة أن يظلم فيزاد عليه في سيئاته ولا يظلم فيهضم في حسناته
Ibn Abbaas (may Allah be pleased with him) said that the son of Adam, on the Day of Judgment, will not fear that he is wronged by having his bad deeds increased. [Nor will he fear] that he has been wronged by having his good deeds destroyed.
[الصحيح المسبور من التفسير بالمأثور – Page 369 Volume 3]
فالظلم : الزيادة بأن يحمل عليه ذنب غيره ، والهضم : النقص
Zulm [in this context] is increase by means of loading upon a person the sins of another. And Al-Hadm means to decrease [i.e. good deeds of a person in this cae].
A person has to be a believer if he wants to be rewarded for his deeds in the next world. No Religion other than Islaam will be accepted on the Day of Judgment. The disbelievers are rewarded for their deeds in full in this world. On the Day of Judgment, they will have no good deeds to their credit.
Those who believe in Allaah and His Messenger (sallallaahu alayhi wa sallam) and do good deeds, then they will receive their recompense in full in the next world. They will not fear that they will be wronged by having their good deeds destroyed or by having their bad deeds increased.