What is the ruling on the prayer of someone who joined the Imam in the third rak'ah and sat for the final tashahhud, this being their first tashahhud? Should they recite the complete tashahhud or without the Ibrahimiyyah prayer, and are their previous prayers valid, or must they be repeated?

The Abrahamic prayer (Salat al-Ibrahimiyyah) is not required in the first tashahhud according to many scholars. Some, however, are of the view that it is required therein. Nevertheless, there is no issue in performing it, even according to the opinion that it is not required. Therefore, all prayers performed in this manner are valid and do not need to be repeated.