Kitzur Shulchan Aruch, 193:1, 12

When a person becomes sick, it is the duty of every one to visit them; for we find that the Holy Blessed One visits the sick. As our Rabbis, of blessed memory, explained the verse: “And the Lord appeared unto him in the planes of Mamre” (Genesis 18:1), from this is inferred that God came to visit Abraham because he was sick. Relatives and friends who are accustomed to visit the sick person's house often should visit as soon as they hear of the sickness. But acquaintances who do not visit regularly should not call immediately, but should wait until three days have elapsed, in order not to spoil the sick person's chance of recovery by casting upon them the designation of an invalid. If, however, one became suddenly ill, even acquaintances should visit immediately. Even a great person should visit a less important person, even many times during the day. One who visits the sick frequently is praiseworthy, providing that their presence should not become troublesome to the invalid. A person should not visit their enemy who is sick and should not comfort their enemy in mourning, for the enemy may think that he rejoices at his calamity. One may, however, attend their enemy's funeral and should not apprehend that people would think that he rejoices at the enemy's downfall, since this is the end of every mortal...The non-Jew should be visited during his illness for the sake of peace. [AJWS translation]