salam. pls dont refer to other answers. is Salah valid if one reads the shortest version of tashahhud in last sitting?

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

The last Tashahhud is one of the pillars of the prayer according to the preponderant view in our opinion, and if someone says its brief form, his prayer is valid.

One of its brief forms is what An-Nawawi mentioned as he said:

"The least form of Tashahhud: Ash-Shaafi’i and most scholars of the Shaafi’i School are of the view that the least form of Tashahhud is: “Attahiyyaatu lillaahi, salaamun `alayka ayyuhan-nabiyyu wa rahmatullaahi wa barakaatuhu, salaamun `alayna wa `ala ibaadillaahis-saaliheen. Ash-hadu alla ilaaha illa Allah, wa anna Muhammadan rasoolu Allah (Glorification is for Allah. May Allaah exalt your mention, O Prophet; mercy and blessings be upon you. Peace be upon us and all of Allah’s righteous slaves. I bear witness that none has the right to be worshipped except Allah and I bear witness that Muhammad is His slave and Messenger.)" [End of quote]

However, it is also obligatory in the last Tashahhud to exalt the mention of the Prophet according to the view that we consider to be the preponderant one as well; it can be achieved by any given form.

An-Nawawi said:

"With regard to the least form of exalting the mention of the Prophet [in Tashahhud], Ash-Shaafi’i and most scholars of the Shaafi’i School are of the view that the least form of exalting the mention of the Prophet is to say: “Allaahumma Salli ‘ala Muhammad.” So if he says: Salla Allahu ‘ala Muhammad: then there are two views about this quoted by the author of Al-Haawi: He said: it is like the two views in his saying ‘Alaykum assalaam; the correct view is that it is sufficient for him. The author of At-Tahtheeb authoritatively mentioned this. This is evidence that if he says: Allaahumma Salli ‘ala An-nabi or said ‘ala Ahmad, then it is sufficient for him. In addition, Ar-Raafi’i authoritatively stated that if he says: Salla Allahu ‘ala rasoolihi, it is sufficient for him. In one view, it is sufficient for him to say: sallallaahu 'alayhi." [End of quote]

For more benefit, please refer to Fatwa 98958.

Allah knows best.