Question:
Prayers performed in Masjid al-Haram in Makkah carry the reward of one hundred thousand prayers. If someone makes a mistake in such a prayer, does that mistake also count as one hundred thousand sins?
Answer:
The answer is no. If a mistake occurs in prayer, Islamic law already provides methods to correct it. For example, if a person forgets something in prayer, he performs Sujūd as-Sahw (the prostration of forgetfulness). Once he corrects the mistake using this method, the prayer becomes valid and the error is removed.
If the mistake is so serious that the prayer becomes invalid, the person simply repeats the prayer correctly. When the correct prayer is performed, the earlier invalid one does not count.
Therefore, there is no need to imagine complicated calculations like “one hundred thousand sins.” The system of correction already exists within Islamic law.