BabylonianTalmud, Nedarim 39b-40a

R. Helbo fell ill. Thereupon R. Kahana went and proclaimed: R. Helbo is sick. But none visited him. He rebuked them [the scholars], saying, ‘Did it not once happen that one of R. Akiva's disciples fell sick, and the Sages did not visit him? So R. Akiva himself entered [his house] to visit him, and because they swept and sprinkled the ground before him, he recovered. ‘My master,’ said he, ‘you have revived me!’ [Straightway] R. Akiva went forth and lectured: He who does not visit the sick is like a shedder of blood. When R. Dimi came, he said: One who visits the sick causes the sick to live, while one who does not causes the sick person to die. How does one cause [this]? Shall we say that one who visits the sick prays that one may live, whilst one who does not, prays that one should die, — ‘that one should die!’ can you really think so? But [say thus:] One who does not visit the sick prays neither that he may live nor die. [Soncino translation. Edited for gender neutrality]