How should one perform the Tashahhud in a three-rak'ah or four-rak'ah prayer, and is it obligatory to recite the entire Tashahhud in the second rak'ah, with evidence from the Book and the Sunnah?

The first tashahhud in a three- or four-rak'ah prayer is obligatory, and it has several forms, including: "All compliments [are] for Allah and prayers and good statements. Peace be upon you, O Prophet, and the mercy of Allah and His blessings. Peace be upon us and upon the righteous servants of Allah. I bear witness that there is no god but Allah, and I bear witness that Muhammad is His servant and His messenger."

Scholars have differed regarding the permissibility of invoking blessings upon the Prophet after the first tashahhud:

First Opinion: It is recommended to invoke blessings upon the Prophet after the first tashahhud. This is the view of Ash-Shafi'i and Ibn Hazm, and it was chosen by Ibn Baz and Al-Albani. Second Opinion: The worshiper should limit the tashahhud to the two testimonies and not add the invocation of blessings upon the Prophet. This is the view of the majority of jurists and was chosen by Ibn 'Uthaymeen, who argued that the Prophet did not teach the Companions to invoke blessings upon him in the first tashahhud.