Which Tashahhud do we recite in Nawafil prayers, or in Shafʿ and Witr?

The Tashahhud (definition) in supererogatory prayers (Nawāfil), Shafʿ, and Witr is the same as the Tashahhud in obligatory prayers (Farāʾiḍ). Various forms have been authentically reported from the Prophet (peace be upon him), among them: - From Ibn Abbas (may Allah be pleased with both of them): "All blessings, prayers, and good things are for Allah. 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 the Messenger of Allah." In another narration: "His servant and Messenger." - From Ibn Umar (may Allah be pleased with both of them): "All salutations are for Allah, and prayers and good things. Peace be upon you, O Prophet, and the mercy of Allah." Ibn Umar said: "I added to it 'and His blessings'." "Peace be upon us and upon the righteous servants of Allah. I bear witness that there is no god but Allah." Ibn Umar said: "I added to it 'alone, without any partner'." "And I bear witness that Muhammad is His servant and Messenger." - From Abu Musa al-Ashʿari: "All blessings, good things, and prayers are for Allah. 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 Messenger." - From Al-Qasim bin Muhammad: "All blessings, good things, prayers, and pure things are for Allah. Peace be upon the Prophet... to the end of Ibn Masʿud's Tashahhud."

The Tashahhud mentioned above is limited to the first Tashahhud in four-unit and three-unit prayers. As for the second Tashahhud in four-unit and two-unit prayers, and Witr, the Salat al-Ibrahimiyyah (Ibrahimic prayer) is added: "O Allah, send prayers upon Muhammad and upon the family of Muhammad, just as You sent prayers upon Ibrahim and upon the family of Ibrahim. Indeed, You are Praiseworthy and Glorious. O Allah, send blessings upon Muhammad and upon the family of Muhammad, just as You sent blessings upon Ibrahim and upon the family of Ibrahim. Indeed, You are Praiseworthy and Glorious."