Musnad Ahmad 31:668

Ishaq ibn Ibrahim al-Razi narrated to us, Salama ibn al-Fadl narrated to us, Muhammad ibn Ishaq narrated to us, from Muhammad ibn Thabit ibn Sharhabil, from Abu Sa’id, the freed slave of al-Mahri, from Abu Sa’id al-Khudri, who said: I heard the Messenger of Allah, peace and blessings of Allah be upon him, say: "Whoever bears with patience the hardships and severity of Medina, I will be an intercessor for him on the Day of Resurrection."