Alleged Contradictions in the Qur'an answer
Concerning the Food for the Inhabitants of Hell

What will be the food for the people in Hell? The food for the people in Hell will be only "Dhari" [Sura 88:6], or only foul pus from the washing of wounds [S. 69:36], or will they also get to eat from the tree of Zaqqum [S. 37:66]? Together, these verses constitute three contradictions.

Verses in question:
88:6 No food will there be for them but a bitter Dari'
69:36-37 "Nor hath he any food except of Ghisleen. None will eat it except the Khati'un. (sinners)
37:62-68. Is that the better entertainment or the Tree of Zaqqum?
For We have truly made it (as) a trial for the wrong-doers.
For it is a tree that springs out of the bottom of Hell-Fire:
The shoots of its fruit-stalks are like the heads of devils:
Truly they will eat thereof and fill their bellies therewith.
Then on top of that they will be given a mixture made of boiling water. Then shall their return be to the (Blazing) Fire.
The first task is to define these three substances found in Hellfire. Imaam Ibn Kathir Ad-Damishqi (d. 1372CE) has given a thorogh discussion of these terms in his renowned Tafsir Al-Qur'an Al-Azim. Concerning the Dari, he writes:
Ali ibn Abi Talhah reported from Ibn Abbas that he said, "A tree from the Hellfire." (fn. At-Tabari 24:383). Ibn Abbas, Mujahid, 'Ikrimah, Abu Al-Jawza' and Qatadah, all said, "It is Ash-Shibriq (a type of plant)." Qatadah said, "The Quraysh called it Ash-Shabraq in the spring and Ad-Dari in the Summer." Ikrimah said, "It is a thorny tree which reaches down to the ground." (fn. At-Tabari 24:384). Al-Bukhari related that Mujahid said, "Ad-Dari is a plant that is called Ash-Shibriq. The people of Hijaz call it Ad-Dari when it dries, and it is poisonous." (fn. Fath Al-Bari 8:570). Ma'mar narrated that Qatadah said, "No food will there be for them but Dari, this is Ash-Shibriq. When it dries it is called Ad-Dari." (fn. At-Tabari 24:384). Sa'id narrated from Qatadah that he said, "No food will there be for them but Dari, this is the worst, most disgusting and loathsome of foods." (fn. At-Tabari 24:384). (Tafsir Ibn Kathir, Abridged, Darussalam Publishers & Distributors, 2000, vol. 10, p. 457)
This detailed discussion clarifies the meaning of the word beyond any doubts. We can conclude that Ad-Dari refers to any of thorny plant, similar to a species know to the Quraysh, while it also carries the wider meaning of a disgusting and loathsome food. Moving on to Ghislin, Imaam Ibn Kathir once again provides a detailed commentary:
Qatadah said, "it will be the worst food of the people of the Hell-fire." (fn. At-Tabari 23:591). Ar-Rabi' and Ad-Dahhak both said, "It (Ghislin) is a tree in Hell." Shabib bin Bishr reported from ikrimah that Ibn Abbas said, 'Ghislin will be the blood and fluid that will flow from their flesh." Ali bin Abi Talhah reported from Ibn Abbas that he said, "Ghislin is the pus of the people of the Hell-fire." (Tafsir Ibn Kathir, Abridged, Darussalam Publishers & Distributors, 2000, vol. 10, p. 148)
The discussion of Ghisleen seems to point out two different views. One is that it is a tree in Hell, while there are other views that it refers to a collection of foul liquids, especially those fluids from the victims of Hell. Meanwhile others refer to it as simply the worst punishment. This information will be useful later on in the discussion. Concerning the Tree of Zaqqum, there is little ambiguity here, and it is sufficient to quote the explanation of Shaykh Umar Sulayman Al-Ashqar, Professor at the University of Jordan, who says:
What we may understand from these âyât is that this tree is a repulsive tree, whose roots go deep into the bottom of Hell, and whose branches stretch forth all over. Its fruits are so ugly that they are likened to the heads of devils, so that everyone may easily understand just how ugly they are, even though they have never seen them. Although this tree is so vile and obnoxious, the people of Hell will become so hungry that they will have no choice but to eat from it until they are full. When they have filled their bellies, this food will start to churn like boiling oil, which will cause a great deal of suffering to them.
(Al-Ashqar, The Final Day : Part 3 - Paradise And Hell In the Light of the Quran and Sunnah, International Islamic Publishing House 2000, p.104)
This is how it has been described in Surat Ad-Dukhan:
44:43-46. Verily, the tree of Zaqqûm, Will be the food of the sinners, Like boiling oil, it will boil in the bellies, Like the boiling of scalding water.
Various Qur'anic commentators mentioned that this will tear up the innards of the inhabitant of Hell. From this verse we note that eating from Tree of Zaqqum gives rise to boiling oil in the internal organs, which tear them apart, releasing bodily fluids. In concluding the descriptions, one should also note that the Hereafter - both Heaven and Hell - is beyond the limits of Human understanding, and therefore these descriptions are only meant to paint a vague idea of the actual torment, for it is torment, the like of which no human mind can conceive.
At this stage, there are several ways of explaining the alleged contradiction.
1. Linguistically, there is no contradiction between only eating Dari, and eating from the Tree of Zaqqum. Ad-Dari is a general term for the thorny plants found in Hell-fire, the greatest of which is the Tree of Zaqqum. There is also no contradiction if we understand Ghisleen to refer to a Tree, as many of the early scholars did. This is what has been narrated from Ar-Rabi and Ad-Dahhak about what verse 69:36 means, as they said, "It (Ghislin) is a tree in Hell."
2. We can also reconcile the verses by seeking a more comprehensive definition of Ghisleen. Muhammad Asad made an interesting comment on the meaning of Ghisleen:
The noun ghislin, which appears in the Qur'an only in this one instance, has been variously - and very contradictorily - explained by the early commentators. Ibn Abbas, when asked about it, frankly answered, "I do not know what ghislin denotes" (Razi). The term "filth" used by me contains an allusion to the "devouring" of all that is abominable in the spiritual sense: cf. its characterization in the next verse as "[that] which none but the sinners eat" – i.e. (metaphorically) in this world, and, consequently, in the hereafter as well. (Asad, Message of the Qur'an, The Book Foundation 2003)
This is a likely explanation since the punishments of Hell-fire are beyond human understanding, and therefore any reference to punishment in Hell is naturally a general reference. It is logical that Ghisleen is a comprehensive term used to refer to filth of any form.
3. Even if we state that Ghisleen does indeed refer to a collection of foul liquids, then it becomes clear that one source of Ghisleen is the Dari plants. In fact, Imaam Abu Abdullah Al-Qurtubi (d. 1272 CE) mentions in his commentary, Al-Jaami'li Ahkaam Al-Qur'aan, the following narration:
Khalid bin Ziyad said: I heard Al-Mutawakil bin Hamdan ask about this verse, "They will not have any food except from Dharee'" He said: It has reached me that Al-Dharee' is a tree in hell-fire [Jahanam] bearing blood and puss, with a bitter taste and that is their food.
Thus, from this explanation of the early scholars it becomes clear that ghisleen is found in the Dari and the Zaqqum. It can be interpreted to describe another aspect of the same food. Therefore, ingesting Dari is equivalent to ingesting Ghisleen.
4. It should also be noted that the meaning of the verse in Arabic is meant to imply that there is no food other than food of such a nature. This is the beauty of the Qur'anic arabic, as Syed Qutb (d. 1966CE) notes:
They are "made to drink from a boiling fountain. Their only food shall be the fruit of Dhari', which will neither nourish nor satisfy their hunger." Dhari' is said to be a tree of fire in Hell. This explanation is based on what has been revealed about the tree of "zayqoom" which grows at the centre of Hell. It is also said to be a kind of cactus thorn, which when green is called "shabraq" and is eaten by camels. However, when it is fully grown it cannot be eaten as it becomes poisonous. Whatever it is in reality, it is a kind of food like "ghisleen" and "shabraq" (names given by the Qur'an to refer to the food available in Hell) which neither nourishes nor appeases hunger.
It is obvious that we, in this world, cannot fully comprehend the nature of that suffering and torture in the hereafter. The description is made in order to give our human perceptions the feeling of the greatest possible pain, which is produced by a combination of humiliation, weakness, failure, the scorching fire, drinking and bathing in boiling water, and eating food unacceptable even to the camels.
From all these aspects we get a feeling of the ultimate affliction. But the affliction of the hereafter is, nevertheless, greater. Its true nature is incomprehensible except to those who will actually experience it. May Allah never count us among them.
Similary, another scholar says:
Here there is a question that some other ayaat are talking about some other type of food people will have in the Hell-fire. Just like inna shajarata zaqqum - a tree that's called az-zaqqum. When Allah SWT says they will have only this thing to eat, it simply means they will have only these type of items in the Hell-fire. Nothing of real food. Everything that they will use for food over there will not be really food, just like they will go to that stream of pus and would start drinking from it - its not food. They would go to those trees that have poisoned fruits, full of thorns, and they will start chewing that - [but] it's not something to eat. So, it simply means nothing that deserves to be used as a food over there. People will just start taking things from here and there, whatever they find they will just start eating those.
Hence, the type of exclusion given in the verses does not exclude substances of a similar nature. If the verses were about this life, and one stated that a group of people would have no food but terrible thorny plants, while another verse stated that the same group would have roast chicken (or some other pleasant food), then it might be a contradiction. However, this is not the case here. The meaning of the Qur'an is clear that no matter what the food, it will be an unbearable torture beyond human imagination.
5. Lastly, it should be noted that there are different levels in Hell, and different groups in Hell. All these groups will recieve different punishments depending on what they deserve. The verse about Ghisleen states that none shall eat it except the khati'un (a category of sinners), who neither believed in Allah nor fed the poor and needy. Meanwhile, the chapter about Dari is only speaking about some people who will enter Naaran Haamiyah (88:2-4), which some scholars describe as a certain level of Hell-fire. As Imaam Al-Qurtubi mentions in his tafsir:
Allah has said: "Therefore he has not here today a true friend, Nor any food save filth" [Al-Haqqah, 35-36] Allah said here "Nor any food save filth" which is different than Ghisleen. It is believed that Hell-fire is made of levels, those who eat from al-zaqoom, those who eat from al-ghisleen, those who eat from Al-dharee', those who drink from hameem, and those who drink from As-sideed. Al-Kalbi said: Al-Dharee' is for those on a certain station [in Hell] and Al-zaqoom are for those on a different station.
Therefore, this explanation from the earliest sources also refutes the alleged contradiction.
These points should demonstrate that these verses do not signify a contradiction at all.