Musnad Ahmad 32:806

Muhammad ibn Ja‘far narrated to us, Shu‘bah narrated to us, from Hisham ibn Zayd, who said: I heard Anas ibn Malik say: The Messenger of Allah (peace and blessings of Allah be upon him) said to the Ansar: "You will encounter selfishness after me, so be patient until you meet me, for your appointed meeting place is the Cistern (al-Hawd)."