How can one reconcile the Hadith (When it [the prayer] is sound, all of his deeds are sound, and if it is corrupt, all of his deeds are corrupted) with the Almighty's saying (He [Allah] does not allow to be lost the reward of any who does good), given the possibility that a Muslim's prayer may not be perfect due to life pressures, and does this lead to the loss of all his good deeds and his being equated with a disbeliever?

Prayer is the greatest pillar of Islam after the two testimonies of faith. Several hadiths have been narrated stating that it is the first thing a servant will be held accountable for on the Day of Resurrection. The correct wording of the hadith (definition) is: "The first thing a servant will be held accountable for on the Day of Resurrection is his prayer. If he has completed it, it will be written for him as complete. If he has not completed it, Allah Almighty will say: 'Look, do you find for My servant any voluntary deeds by which you may complete his obligatory deeds?' Then similarly with Zakat (definition), and then deeds will be taken into account accordingly."

The meaning of the hadith is that the deficiencies in obligatory deeds (such as prayer and Zakat) are made up for by voluntary and supererogatory acts. Scholars have differed on what is meant by "deficiency": Is it exclusive to those who forgot or were negligent unintentionally, or does it also include those who were deliberate? The more apparent opinion is that it includes both the deliberate and the non-deliberate.

As for the interpretation of the hadiths that indicate the corruption of all other deeds by the corruption of prayer, they are: 1. They were issued as a form of deterrence and warning against negligence. 2. They indicate a strict reckoning and intolerance regarding other deeds. 3. They apply to those who abandon prayer entirely, or whose prayer is not accepted at all, and thus the evidences align.

In summary: Whoever falls short in some obligatory acts or duties of prayer due to forgetfulness, their deficiency is made up for by supererogatory prayers. As for one who abandons prayer entirely, they are in grave danger, and to them apply the narrations indicating the non-acceptance of their other deeds.