When is the prostration of forgetfulness (sujud al-sahw) performed before the salutation (taslim) and when is it performed after it? Is the tashahhud prescribed for the prostration of forgetfulness? And what is the authenticity of the hadith about praying four rak'ahs before sleeping, reciting specific surahs in each rak'ah?

Scholars have differed regarding the prostration of forgetfulness (sujud al-sahw), and the preponderant opinion is that there is no tashahhud after the two prostrations of forgetfulness. As for the aforementioned hadith about praying four rak'ahs after the 'Isha prayer and its virtue, it is weak, but it is permissible to act upon it concerning virtuous deeds. It indicates the permissibility of praying four or six rak'ahs after the 'Isha prayer.