Musnad Abu Ya'la al-Mawsili 42:249

Zuhayr narrated to us, Yazid bin Harun narrated to us, Hammam bin Yahya informed us, from Qatadah, from Abu Isa al-Aswari, from Abu Sa’id al-Khudri, from the Prophet (peace be upon him), who said: "Visit the sick and follow the funeral processions, for they remind you of the Hereafter."