The Qur'an makes the following statements regarding the food that unbelievers will have in hell:
No food will there be for them but a bitter Dhari S. 88:6 Y. Ali
Nor hath he any food except the foul pus from the washing of wounds, S. 69:36 Y. Ali
In a footnote, Yusuf Ali gives the following explanation for Dhari:
It is a plant, bitter and thorny, loathsome in smell and appearance, which will neither give fattening nourishment to the body nor in any way satisfy the burning pangs of hunger. ...
Other translators render the term as "bitter thorn-fruit" (Pickthall) "dry, bitter and thorny herbage" (Sher Ali), "cactus thorn" (Arberry), "the foul thorn" (Palmer).
Obviously, both kinds of ‘food’ are chosen to evoke a feeling of horror when thinking about Hell. However, the contradiction is in the double claim that this or that will be the only food, i.e.
There is yet another passage that is relevant to this discussion:
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. S. 37:62-68 Y. Ali; cf. 56:52
Thus, regarding this one topic alone, the Qur'an contains three contradictions:
Contradictions in the Qur'an
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