Sunan Abi Dawud 974
سنن أبي داود#974SahihIbn ‘Abbas said:The Messenger of Allah( may peace be upon him) used to teach us the tashahhud as he would teach us the Qur’an, and would say: The blessed adoration of the tongue, acts of worship (and) all good things are due to Allah. Peace be upon you, O Prophet, and Allah’s mercy and His blessings. Peace be upon us and upon Allah’s upright servants. I testify that there is no god but Allah, and I testify that Muhammad is Allah’s apostle (peace be upon him)
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Al-AlbaniSahih
Muhammad Muhyi Al-Din Abdul HamidSahih
Shuaib Al ArnautSahih
Zubair Ali ZaiSahih Muslim (403)
In-book reference: 2:585