Hadith 269

وعن ثوبان عن النبي صلى الله عليه وآله وسلم أنه قال : « لكل سهو سجدتان بعدما يسلم ». رواه أبو داود وابن ماجه بسند ضعيف.
Narrated Thawban (RA): The Prophet (ﷺ) said: "There are two prostrations after the Taslim (salutation) for each forgetfulness." [Abu Dawud and Ibn Majah reported it through a weak chain of narrators].
Hadith Reference بلوغ المرام / 269
Hadith Grading محدثین: حسن
Hadith Takhrij «أخرجه أبوداود، الصلاة، باب من نسي أن يتشهد وهو جالس، حديث:1038، وابن ماجه، إقامة الصلوات، حديث:1219* إسماعيل بن عياش رواه عن أهل بلده وصرح بالسماع فلا وجه لتضعيف السند.»
Related hadith on this topic
Explanation & Benefits
Maulana Ataullah Sajid
Benefits and Issues:

➊ The meaning of every forgetfulness is that the mistake, whether it is of omission or addition, can be rectified by two prostrations of forgetfulness (sujud as-sahw).

➋ If it becomes certain that fewer units (rak‘ahs) of the prayer have been performed, then the missed rak‘ah should be performed and then the prostration of forgetfulness (sujud as-sahw) should be done, as has been explained in previous chapters.

➌ The prostrations of forgetfulness (sujud as-sahw) can be performed before the salutation (salam) as well as after it. The meaning of the hadith under study is not that sujud as-sahw cannot be done before the salam, but rather that in every case of forgetfulness, it is also correct to perform the prostrations after the salam.
Source: Commentary on Sunan Ibn Mājah by Mawlānā ‘Atā’ullāh Sājid, Page: 1219