Abu Bakr bin Muhammad bin Amr bin Hazm (may Allah have mercy on him) went to visit Umar bin al-Hakam (may Allah have mercy on him) when he was ill. Abu Bakr said: O Abu Hafs! Narrate to us a hadith about which there is no disagreement. He said: Sayyiduna Ka'b bin Malik (may Allah be pleased with him) told me that the Prophet (peace and blessings be upon him) said: "Whoever visits a sick person enters into mercy, and when he sits with him, he seeks intercession in it (that mercy)."
Hadith Referenceالمعجم الكبير للطبراني / باب الكاف / 16254