Has it been narrated in the Prophetic Sunnah that which the Ibadhi brother did, by not sitting for the final Tashahhud after the Imam's Tasleem, and standing up to complete his prayer, then making one Tasleem without Tashahhud?

Scholars have differed regarding the ruling on the final Tashahhud. The Shafi'is and Hanbalis hold that it is a pillar (rukn) of prayer, basing their argument on the hadith of Ibn Mas'ud (may Allah be pleased with him): "before the Tashahhud was obligated upon us." The Malikis and Hanafis are of the view that sitting for the duration of the Tashahhud is obligatory, but not the Tashahhud itself. The well-known opinion from Malik is that what is obligatory is merely sitting for the duration of the Taslim (salutation). They cite the hadith of the one who prayed incorrectly as their evidence. The Shafi'is countered that the Tashahhud was not mentioned because it was already known. The preponderant opinion is that of the Shafi'is and Hanbalis, who consider it obligatory. Therefore, whoever intentionally or unintentionally omits it and does not make it up, their prayer is invalidated.