Yahya related to me from Malik that he had heard from Jabir ibn Abdullah that the Messenger of Allah, may Allah bless him and grant him peace, said, "When a man visits an invalid, he plunges into mercy to the extent that when he sits with him, it settles in him," or the like of that.
Muwatta Malik Book 50, Hadith 18
← Previous Hadith Malik related to me from Nafi from Ibn Umar that the Messenger of Allah, may Allah bless him and grant him peace, said, "Fever is from the vehemence of the heat of Jahannam, so put it out with water."

Muwatta Malik Book 50, Hadith 17 Next Hadith → "There is no contagion, no hama and no serpent in a hungry belly. However, the possessor of sick livestock must not stop at the same place as the possessor of healthy livestock, but the possessor of healthy livestock may stop wherever he wishes."

They said, "Messenger of Allah, Why is that?" The Messenger of Allah, may Allah bless him and grant him peace, said, "It is harmful."

Note: The majority of scholars interpret this to mean that these things in and of themselves do not transmit or cause harm through supernatural or hidden means but that Allah is ultimately in control and any fearful superstition around these is false.

Muwatta Malik Book 50, Hadith 19