How is prayer corrected when in doubt about the number of rak'ahs, is it by saying the tasleem and performing the prostration of forgetfulness, or by finishing the prayer and then performing the prostration of forgetfulness?

The prostration of forgetfulness (sujood as-sahw) is required when there is an addition, omission, or doubt in the prayer. Doubt is defined as hesitation between two probable matters. Whoever doubts after the salutation (tasleem) should not pay attention to his doubt unless there is definitive proof, otherwise, it would open the door to obsessive whispering (waswasa). As for whoever doubts during the prayer, there are two situations:

1. If one of the two matters predominates in his mind: He acts upon what predominates in his mind and performs the prostration of forgetfulness after the salutation.

2. If nothing predominates in his mind: He builds upon the lesser (the smaller number of rak'ahs) and completes his prayer, and performs the prostration of forgetfulness before the salutation.