Musnad Ahmad 830:76

Aswad ibn Amir narrated to us, Hammad ibn Salamah informed us, from Yunus ibn Ubayd, from al-Hasan, from Abu Bakrah, and from Muhammad ibn Sirin, from Abu Bakrah, that the Messenger of Allah (peace and blessings of Allah be upon him) said: "Do not return after me as disbelievers, striking the necks of one another." And Ibn Sirin said: "As those who have gone astray, striking the necks of one another."