Musnad Ahmad 30:2642

Waki’ narrated to us, from Aflah, from Abu Bakr ibn Muhammad ibn ‘Amr ibn Hazm, from Salman al-Agharr, from Abu Hurairah, from the Prophet (peace and blessings of Allah be upon him), who said: "Whoever bears the hardship and severity of Medina, I will be an intercessor for him—or a witness—on the Day of Resurrection."