Salam in the prayers

1114. While a person sits after reciting Tashahhud in the last Rak'at, and his body is tranquil, it is Mustahab to say:Assalamu ‘Alayka Ayyuhan Nabiyyu wa Rahmatullahi wa Barakatuh.
Then it is obligatory to say: Assalamu Alaykum Wa Rahmatullahi Wa Barakatuh.

Or alternatively, he can say: Assalamu Alayna Wa Ala Ibadi llahis Salihin.

But if he recites this Salam, then as per obligatory precaution, he must follow it up with saying: Assalamu Alaykum Wa Rahmatullahi Wa Barakatuh.

Although the obligation of saying “Wa Rahmatullahi Wa Barakatuh” is as per precautionary measure.

1115. If a person forgets the Salam of prayers, and remembers when the form of Namaz has not be disrupted, nor has he performed any act, which if done intentionally or forgetfully, invalidates the prayers e.g. turning away from Qibla, he should recite the Salam and his prayers will be valid.

1116. If a person forgets the Salam of prayers, and remembers after the form of prayers has been disrupted; if he has not performed any act, which if done intentionally or forgetfully, invalidates the prayers e.g. turning away from Qibla, he should recite the Salam and his prayers will be valid. And if he has performed an act which if done intentionally or forgetfully, invalidates the prayers, his prayers is void.