Adi reported from the Prophet ﷺ that he said, "Woe to you," or "Woe upon you." Shuba said, He was uncertain which. "Do not revert to disbelief after me, striking one another's necks."
عن النبي ﷺ قال: ويلكم أو ويحكم- قال شعبة: شك هو- لا ترجعوا بعدي كفارا، يضرب بعضكم رقاب بعض.
Bukhari narrated it in al-Adab (6166) and Muslim in al-Iman (66), both from the hadith of Shubah, from Waqid bin Muhammad, that he heard his father narrating from Abdullah bin Umar, and he mentioned it.