Musnad Ahmad 937:271

Yahya ibn Adam narrated to us, Zuhayr narrated to us, from Mutarrif ibn Tarif, from Abu al-Jahm, from Khalid ibn Wahban, from Abu Dharr, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Whoever separates from the community by a span, he has cast off the yoke of Islam from his neck."