Surah Al-Kahf (18) — Ayah 21

21. Thus We made the people [19] aware of them so that they might know that Allah's promise is true and that there is no doubt about the coming of the Hour [20]. When they were disputing among themselves about their case, some said, "Build a structure over them." Their Lord knows best about them. But those who prevailed in the matter said, "We will surely build a mosque [21] over them."

[19]
The Change of Kingdom and Favorable Circumstances:

When the one who brought the food reached the city, the world there had completely changed. There was a marked difference in the people's culture and civilization, clothing, and appearance. The language had also changed considerably, and when people saw this young man, everyone turned their attention towards him, but he kept avoiding them. Then, when he presented a coin from several centuries ago while buying food, the shopkeeper and all those around began to look at this young man with suspicion. They suspected that perhaps this person had found some ancient treasure. Therefore, on the basis of this suspicion, people caught him and presented him before the higher authorities. And when this young man gave his statement, it became clear that these were the very followers of Christ who had suddenly disappeared several centuries ago, and whose record had been continuously transferred in the government offices until now. This news spread instantly throughout the Christian population. The very thing they wanted to avoid, Allah made everyone aware of their condition. The difference was that when they had fled and disappeared, at that time they were considered criminals by that society and government, but now, in everyone's eyes, they were respected for remaining steadfast in their faith.

[20]
The Nature of the Dispute About Resurrection After Death: Spiritual or Physical?

In those days, although the official religion was Christianity and Christians believed in the Resurrection and the Day of Judgment, nevertheless, strange and philosophical debates were ongoing regarding the Day of Resurrection. Some irreligious people outright denied resurrection after death, as such people are found in every religion, whether this denial is in practice or in words. Among those who believed in resurrection after death, there was a difference of opinion as to whether it would be spiritual or physical, and debates were held on this, but no final decision was being reached. The king himself wanted a final decision on this difference. During those days, the issue of the discovery of these young men came before everyone, which provided undeniable proof of the physical nature of resurrection after death.

[21]
Construction of a Mosque as a Memorial:

Now these Companions of the Cave were respected in everyone's eyes and began to be considered as friends of Allah (awliya Allah). Whether people went to the cave to meet them or not, or whether these people came out of the cave to greet the people or not, this detail is not mentioned anywhere. However, the predominant opinion seems to be that the one who brought the food also went back into the cave, they lay down as before, and there their souls departed from their physical bodies. People thought that these were all sacred personalities, so a memorial building should be constructed at this cave. Then there was a difference of opinion as to what kind of memorial should be built, and the opinion of those who were influential and powerful prevailed, and that opinion was that a mosque or place of worship should be built as a memorial near the cave, which these influential people themselves took responsibility for building. In this way, the Companions of the Cave attained the status of friends of Allah, and their cave became like a shrine or their tomb. Building a mosque or place of worship near or on shrines, khanqahs, or tombs, or making a grave in a mosque considering someone a friend of Allah, are such acts that the Messenger of Allah ﷺ strictly forbade. The reason is that such acts open many doors to shirk (polytheism), as is clear from the following hadiths.

1.
Building Mosques on Graves is an Ancient Polytheistic Practice:

Sayyida Aisha Siddiqa ؓ narrates that some of the pure wives mentioned to the Messenger of Allah ﷺ that they had seen a church named "Maria" in Abyssinia in which there were statues. He ﷺ said: "When a righteous man among them died, they would build a mosque on his grave. Such people are the worst of creation in the sight of Allah." [مسلم، كتاب الصلوٰة]

And Imam Bukhari has mentioned this hadith as follows: Sayyida Aisha ؓ narrates that Umm Habiba ؓ and Umm Salama ؓ mentioned to the Prophet ﷺ a church they had seen in Abyssinia and that there were images in it. He ﷺ said: Their custom was that when a righteous man among them died, they would build a mosque on his grave and place images in it. On the Day of Resurrection, these people will be the worst of all creation in the sight of Allah. [بخاري، كتاب الصلوة، باب هلے نبش قبور مشركي اهل الجاهليه۔ نيز باب الصلوة فى البيعة]

2.
Hadiths Related to Graves:

Sayyida Aisha Siddiqa ؓ narrates that the Messenger of Allah ﷺ, in the illness from which he did not recover, said: "May Allah curse the Jews; they made the graves of their prophets into mosques or places of prostration." Sayyida Aisha ؓ says: If I had not feared that people would make your ﷺ grave a place of prostration, it would have been made accessible to all. [بخاري، كتاب المغازي۔ باب مرض النبيﷺ]

The explanation is that the blessed grave of the Messenger of Allah ﷺ was in the house of Sayyida Aisha ؓ. The arrangement was such that the grave was at the back, then Sayyida Aisha's ؓ residence in front of it, and then the outer door, and except for Sayyida Aisha ؓ or relatives, no one else could go to the grave because there was a wall behind the grave. For this reason, Sayyida Aisha ؓ says that if there had been no fear that after some time people would start prostrating to your grave, the back wall would have been opened for visitation.

3. In the following hadith, besides the grave-worshipping Jews, Christians are also mentioned: Sayyida Aisha ؓ and Sayyiduna Ibn Abbas ؓ both narrate that when the Prophet ﷺ fell ill and signs of death appeared, he would cover his face with his sheet, and when the discomfort increased, he would remove it from his face and say: May Allah curse the Jews and Christians; they made the graves of their prophets into mosques or places of prostration. By this statement, he ﷺ was warning us against the evil deed that the Jews and Christians had done. [بخاري۔ حواله ايضاً]

4. And in Sahih Muslim, Book of Prayer, in the narration of Sayyiduna Jundub, the graves of saints are also mentioned along with the prophets. The words are: "Beware! Those before you made the graves of their prophets and righteous men into places of prostration. Beware! Do not make graves into places of prostration. I forbid you from this."

5. Sayyiduna Abu Sa'id Khudri ؓ says that the Messenger of Allah ﷺ said: "The whole earth is suitable for prayer except graveyards and bathhouses." [ترمذي، ابو داؤد، دارمي، بحواله مشكوة، كتاب الصلٰوة باب المساجد و مواضع الصلوٰة فصل ثاني]

6. The Messenger of Allah ﷺ said regarding himself: "Do not make my grave an 'Eid (festival, urs, or fair), and wherever you are, send blessings upon me. Your blessings are conveyed to me." [نسائي بحواله مشكوٰة۔ باب الصلوٰة على النبيﷺ و فضلها۔ فصل ثاني]

7. And he ﷺ also prayed to Allah: "O Allah! Do not make my grave an idol (shrine) that people come to worship." [مالك، بحواله مشكوٰة، كتاب الصلوٰة، باب المساجد و مواضع الصلوٰة، تيسري فصل]

From all these hadiths, it is clear that the Messenger of Allah ﷺ forbade people from gathering at graves, tombs, shrines, or mausoleums considering them sacred, holding urs or fairs there, and even performing prayers there. Building a mosque on any grave, tomb, or shrine is forbidden because this is done solely out of reverence for the occupant of the grave, and prayer is not valid in a graveyard. Whereas, in our society, it is customary that every shrine has a mosque, or a saint is buried in a mosque. All such situations are prohibited. Those who gather at shrines do so believing those saints to be fulfillers of needs and removers of difficulties. They also perform such rituals or acts of worship there that are only appropriate for Allah or for the House of Allah, such as making vows, offerings, i.e., financial sacrifices. Cleaning graves, decorating them, illuminating them—all these are forbidden by Shariah, yet are practiced there. And some unfortunate people even circumambulate graves like the Ka'bah, cover them with cloths, and do not even refrain from prostrating to them. And probably these are the reasons why prayer in graveyards is prohibited and the construction of shrines and mausoleums is declared forbidden. Nowadays, at some shrines, even the full rituals of Hajj are performed instead of urs, and it is even called Hajj.