Musnad Abu Ya'la al-Mawsili 42:347

Zuhayr narrated to us, Affan narrated to us, Hammam narrated to us, Qatadah narrated to us, from Abu Isa al-Aswari, from Abu Sa’id al-Khudri, that the Prophet (peace and blessings of Allah be upon him) said: "Visit the sick, and follow the funeral processions, for they will remind you of the Hereafter."