In supererogatory prayers, is the tashahhud recited after every two rakʿahs, or only after the last two rakʿahs, and to which part of the tashahhud does it extend? And in obligatory four-unit prayers, is the first tashahhud complete, or only up to "I bear witness that Muhammad is His servant and His messenger"?

In every prayer that has two tashahhuds (whether obligatory or supererogatory), one should limit the first tashahhud (definition) to reciting the tashahhud itself, without invoking blessings upon the Prophet, peace be upon him. This is the view held by most scholars. The Malikis, however, went further, considering it disliked to supplicate after the first tashahhud, even if it is to invoke blessings upon the Prophet, peace be upon him. As for the final tashahhud, there is no disagreement regarding the permissibility of invoking blessings upon the Prophet, peace be upon him, thereafter. However, they differed on whether it is a pillar (integral part) of the prayer. The Hanafis and Malikis held that it is a sunnah (definition) (recommended act), while the Hanbalis and Shafi'is held that it is a pillar.