The Messenger of Allah said: "Do not revert to disbelievers after I am gone." It is Mursal.
Sunan an-Nasa'i Book 37, Hadith 164
← Previous Hadith "The Messenger of Allah said: 'I do not want to see you after I am gone reverting to disbelievers, striking the necks of one another (killing one another). No man is punished for the crime of his father, or the crime of his brother.'" This is correct.

Sunan an-Nasa'i Book 37, Hadith 163 Next Hadith → The Prophet said: "Do not revert to misguidance after I am gone, striking the necks of one another (killing one another)."

Sunan an-Nasa'i Book 37, Hadith 165