Bukhari

Hadith Commentary: Benefits and Issues: ➊
The title of the king of Abyssinia is "Najashi."
And every king of Abyssinia was called Najashi.
And the Najashi who became Muslim and died during the lifetime of the Prophet sallallahu alayhi wa sallam was Ashamah, whose death occurred in Rajab, 9 AH.

➋
This hadith proves that if a person passes away whose status and rank are acknowledged by the Muslim community due to his virtues and excellence, and everyone is indebted to his favors, then his funeral prayer in absentia (salat al-janazah al-gha'ib) should be performed.
Hafiz Ibn Taymiyyah rahimahullah and Hafiz Ibn Qayyim rahimahullah have adopted this moderate position.
There is a difference of opinion among the four Imams (a’immah arba‘ah) on this matter.
According to Imam Shafi‘i rahimahullah and Imam Ahmad rahimahullah, the funeral prayer in absentia is permissible, because according to Imam Shafi‘i rahimahullah, the funeral prayer is a supplication (du‘a), and supplication can be made for both the present and the absent.
Hafiz Ibn Qayyim rahimahullah states:
During the lifetime of the Prophet sallallahu alayhi wa sallam, many of his companions passed away in absentia,
but the Prophet sallallahu alayhi wa sallam did not perform the funeral prayer in absentia for anyone.
The summary is that performing the funeral prayer in absentia as an acknowledgment of the services of a great personality is correct, but it is not correct for every pious person.

➌
The four Imams (a’immah arba‘ah) are in agreement that there are four takbirs in the funeral prayer.

Benefits and Issues:
➊
The connection of the sick person with the Fire of Hell is unseen and spiritual. Its reality cannot be known. Or it means that it reminds one of Hell. Or, just as the joys and comforts of this world have a certain relation to the blessings of Paradise, similarly, sorrow and pain have a connection with Hell.

➋
The remedy for heat is water. In most types of fever, the use of water is beneficial.

➌
The method of using water is not specified in this hadith; there can be various ways of using it. For example, drinking water, placing wet cloths on the body, or performing ritual bath (ghusl), as the Messenger of Allah (sallallahu alayhi wa sallam) performed ritual bath (ghusl) in the last days of his blessed life so that the heat would lessen and he could join the congregational prayer. Especially in hot regions, fever is generally due to the intensity of heat. Therefore, treating it with water is appropriate. Asma bint Abi Bakr (radi Allahu anha) used to pour water into the collar of a woman suffering from fever so that the body would cool down, and she used to say that the Messenger of Allah (sallallahu alayhi wa sallam) commanded us to cool it (the fever) with water. (Sahih al-Bukhari, Book of Medicine, Chapter: Fever is from the heat of Hell, Hadith: 5724)