What are the origins and status of the Sunni hadith "Upon you is to follow my sunnah and the sunnah of the rightly guided caliphs after me"?
This hadith has been reported in the Jami' al-Tirmidhi, Sunan Abi Dawud, Sunan Ibn Majah, Musnad Ibn Hanbal and Mustadrak al-Hakim. There are eight chains of transmission of this hadith, all going back to the sahabi 'Irbad Ibn Sariah, none of them is authentic even according to Sunni standard. The hadith therefore cannot be technically relied upon. As far as its content, following the sunna of the Prophet and his successors after him has been established via other widely-reported and more established narrations.
With prayers for your success.