Musnad Ahmad 175:34

Yunus narrated to us, he said: Abu Ma’shar narrated to us, from ‘Abd al-Rahman ibn ‘Abd Allah al-Ansari, who said: Abu Bakr ibn Muhammad ibn ‘Amr ibn Hazm entered upon ‘Umar ibn al-Hakam ibn Thawban and said: "O Abu Hafs, narrate to us a hadith from the Messenger of Allah, peace and blessings of Allah be upon him, in which there is no disagreement." He said: Ka’b ibn Malik narrated to me, he said: The Messenger of Allah, peace and blessings of Allah be upon him, said: "Whoever visits a sick person wades into mercy. When he sits with him, he becomes submerged in it, and you have become submerged, if Allah wills, in mercy."