In plain words, the Qur’an says that one of the righteous men of God’s servants
saw the sun set in a certain place of the earth—in particular a well full of
water and mud. There, this man found some people. Let us read what is recorded
in the Qur’an (chapter "the Cave", verse 86),
"When he reached the setting place of the sun, he found it setting in a muddy
spring and found a people thereabout. We said: ‘O Dhul-Qarneyn! Either punish or
show them kindness"’ (Surah 18:86).
Lest I failed to understand what the Qur’an meant by these strange words, I
referred to the famous students of the Qur’an as well as to the ancient scholars.
I discovered that all of them concurred with this rendering and said that
Muhammad’s friends inquired about the sunset and that he gave them that answer.
All the scholars such as the Baydawi, Jalalan, and Zamakhshari confirm it. The
Zamakhshari remarks in his book, "the Kash-shaf",
"Abu Dharr (one of Muhammad’s close companions) was with Muhammad during the
sunset. Muhammad asked him: ‘Do you know, O Abu Dharr where this sets?’ He
answered: ‘God and His apostle know better.’ Muhammad said: ‘It sets in a spring
of slimy water"’ (3rd Edition, Volume 2 p. 743,1987).
In his book, "The Lights of Revelation" (p. 399), the Baydawi indicates,
"The sun sets in a slimy spring; that is, a well which contains mud. Some of the
readers of the Qur’an read it, ‘...a hot spring’, thus the spring combines the
two descriptions. It was said that Ibn ’Abbas found Mu’awiya reading it (as)
hot. He told him, ‘It is muddy.’ Mu’awiya sent to Ka’b al-Ahbar and asked him,
‘Where does the sun set?’ He said in water and mud and there were some people.
So he agreed with the statement of ibn al-’Abbas. And there was a man who composed
a few verses of poetry about the setting of the sun in the slimy spring."
The Jalalan (p. 251) says that the setting of the sun is in a well which contains
a murky mud. We found the same interpretation and text in the Tabari’s
commentaries (p. 339) as well as in "Concise Interpretation of the Tabari"
(p. 19 of part 2) in which he remarks that the well in which the sun sets
"contains lime and murky mud".
These are the comments of the pillars of Islam and the intimate companions
of Muhammad such as ibn Abbas and Aba Dharr. Also it is obvious from the
Qur’an (chapter 36:38) that the sun ran then settled down. The verse says:
"And the sun runs on into a resting place."
On page 585, the Baydawi says,
"The sun runs in its course to a certain extent then it stops. It is similar to
the passenger’s repose after he completes his journey" (refer also the book of
al-Itqan by the Suyuti, p. 242).
This is the story of the setting of the sun in the well and its course as a
Taken from http://answering-islam.org/BehindVeil/btv6.html#CH6 (Note: We do not necessarily endorse this site or its views.)