What is the ruling on one who frequently doubts during prayer? Is the prostration about which he doubts considered the second one? What should he do if he doubts the number of rak'ahs? And is he required to perform the prostration of forgetfulness (sujud al-sahw)?

Obsessive doubt (shakk mustankah) should be ignored. If a worshiper experiences doubts about the number of prostrations (sajadat) or cycles (rak'at), they should disregard them and continue their prayer. Prostration of forgetfulness (sujud as-sahw) is not obligatory in this case; rather, it is recommended according to many scholars.