For what reasons is the prostration of forgetfulness (sujūd al-sahw) required? How is sujūd al-sahw performed?

It is obligatory to perform the prostration of forgetfulness (sujūd al-sahw) in order to compensate for deficiencies that occur in prayer due to unintentionally delaying, repeating, or advancing an essential pillar (rukn), or omitting, delaying, or altering a necessary act (wājib) (el-Fetâva’l-Hindiyye, 1/125 ff.).

The method of performing sujūd al-sahw is as follows: In the final sitting of the prayer, after reciting the tashahhud (tahiyyāt), one gives salām to the right side, and without any pause, says "Allāhu akbar" and goes into prostration. In this position, "Subhāna rabbiyal-a‘lā" is recited three times. Then, saying "Allāhu akbar," one sits up, and again, saying "Allāhu akbar," goes into a second prostration, reciting "Subhāna rabbiyal-a‘lā" three times. After saying "Allāhu akbar," one sits again. In this sitting, the supplications "Ettehiyyâtü, Allahümme salli, Allahümme bârik, and Rabbenâ..." are recited, and then salām is given first to the right and then to the left. It is also permissible to recite the salli-bārik and other supplications during the sitting before going for sujūd al-sahw.

Although there are opinions that sujūd al-sahw can be performed after giving salām to both sides, the majority (jumhūr) prefer that it be performed after giving salām only to the right side (Mevsılî, el-İhtiyâr, 1/72-73; el-Fetâva’l-Hindiyye, 1/125; Ibn ‘Ābidīn, Reddü’l-muhtār, 2/77-78). In congregational prayers, in order to prevent the congregation from dispersing by mistake, it is more virtuous and prudent to perform sujūd al-sahw after giving salām only to the right side.

Source: T.C. Diyanet İşleri Başkanlığı, Din İşleri Yüksek Kurulu