Is prostration of forgetfulness (sujud al-sahw) sufficient if a worshipper recites half of the first tashahhud and then says the taslim, or must the prayer be repeated?

If the inquirer read half of the Tashahhud up to "I bear witness that there is no god but Allah, and I bear witness that Muhammad is His servant and Messenger," then made the tasleem (salutation), and then performed the prostration of forgetfulness (sujood al-sahw), his prayer is valid according to most jurists. This is because what comes after this part is not obligatory, except for the salat (invoking blessings) upon the Prophet (peace be upon him), regarding which there is a difference of opinion among jurists. However, if he made the tasleem before performing the Tashahhud and the salat upon the Prophet (peace be upon him) and a long interval passed, he must repeat the prayer because the final Tashahhud is a pillar ( rukn) that cannot be compensated for by prostration.