“Whoever visits a sick person will remain in the harvest of Paradise.” It was said: “O Messenger of Allah, what is the harvest (khurfa) of Paradise?” He said: “Its fruits.”

Narrated by Muslim (no. 2568), from the narration of Thawbān (may Allah be pleased with him).
And in another wording of his: “Until he returns.”

Brief Explanation of the Hadith

The texts of the Sunnah have clarified the rights of a Muslim over his brother, among them: visiting him when he is sick. The Sharīʿah has promised immense reward for this act. Among such narrations is what the Prophet –may Allah’s peace and blessings be upon him– said: “Whoever visits a sick person…”.
Here, the Prophet likened the reward attained by the visitor to that of one harvesting the ripe fruits of Paradise. Thus, whoever goes out to visit a sick person is in the “picking” and gathering of reward until he returns, as mentioned in the other narration.
Al-Khurfah refers to fruit when it ripens, and janāhā means what is gathered from it.
The point, then, is that visiting the sick is a gate of mercy, compassion, and unity. It comforts the patient and eases his pain, and it is one of the rights of a Muslim over his fellow Muslim. It is a confirmed Sunnah, though some scholars considered it a communal obligation (farḍ kifāyah).
Its recommendation is not limited to Muslims only, but extends even to non-Muslims if their guidance to Islam or sincere counsel is hoped for—just as the Prophet –may Allah’s peace and blessings be upon him– visited a Jewish boy during his illness.
Furthermore, among the etiquettes of visiting the sick are: choosing an appropriate time, keeping the stay brief if it burdens the patient, speaking gently, bringing joy to him, praying for him, reminding him of patience and good expectation of Allah, and being considerate of his privacy and that of his family.
In summary, the meaning is that the one who visits a sick person reaps continuous reward—from the moment he leaves his home intending the visit, while sitting with the patient, until his return. Visiting the sick is a simple act, yet its reward with Allah is immense.
In this ḥadīth is encouragement to visit the sick, along with clarification of its great virtue and the immense reward that follows it, and that it is among the deeds by which Paradise may be attained.
It also shows that even simple actions, when accompanied by sincerity and adherence to Prophetic guidance, have a tremendous effect and reward.