What should a worshipper do if they doubt the number of rak'ahs, and does the ruling differ if the doubt occurs before or after the taslim?

If the worshipper doubts the number of rak'ahs after the prayer, he should not pay attention to it. However, if the doubt occurs during the prayer, he should build upon what he is certain of and perform the prostration of forgetfulness (sujud al-sahw) before the salutation (taslim).