How is the funeral prayer performed for a body whose owner’s faith is unknown?

The questioner : Here is a question that arises now because there are people among the apostates whom no one knows about. There are, for example, people who do not pray, and it is well known that whoever dies while not praying is a disbeliever. It is not permissible to pray over him, nor to supplicate for mercy for him. It is not permissible for his family, who know that he died while not praying, to wash him, shroud him, or bring him to the Muslims to pray over him. Rather, it is obligatory for them to take him out to a place, dig a grave for him, and bury him there. This is because he is a disbeliever. And Allah the Exalted said to the Prophet (peace and blessings be upon him): Why? Because they disbelieved in Allah and His Messenger, and they do not come to prayer except while lazy, and they do not spend . This is because, unfortunately, there are now people who die while not praying, and a person is brought to you and you are in doubt about him. So what do you do if a man is brought to you and you do not know whether he is a Muslim or not?

The Shaykh : The answer to this is that we say that Ibn al-Qayyim, in his book *I‘lam al-Muwaqqi‘in*, mentioned that his Shaykh, Shaykh al-Islam Ibn Taymiyyah (may Allah have mercy on him), had difficulties with certain issues in knowledge, and that he saw the Prophet (peace and blessings be upon him) in a dream and asked him about these issues. Among them was the fact that he was grateful to Shaykh al-Islam Ibn Taymiyyah for the fact that funerals were brought to him and he did not know whether they were Muslims or non-Muslims?
The answer was: “It is upon you with the condition, Ahmad.” Ahmad is the name of Shaykh al-Islam Ibn Taymiyyah. The Messenger (peace and blessings be upon him) said to him in the dream: “It is upon you with the condition, O Ahmad.” The meaning of “it is upon you with the condition” is to make a condition in the supplication. So say: “O Allah, if he was a believer, then forgive him and have mercy on him,” and so on. Making a condition in supplication with this exception is permissible. In the Qur’an, Allah the Mighty and Majestic says in the story of the two who swore oaths (li’an) that the woman says, and the man says, “And the curse of Allah be upon him if he is among the liars,” and the woman says, “And the anger of Allah be upon her if she is among the truthful ones.”
And in the Sunnah, the Prophet (peace and blessings be upon him) narrated the story of the companions of the cave who were trapped, and they sought nearness to Allah through their good deeds. They said in their seeking nearness: “O Allah, if I did that for Your sake, then relieve us from what we are in.” This is a conditional supplication, so conditional supplication is permissible. This dream that Shaykh al-Islam saw is a dream that is attested to by the Book and the Sunnah, so it is considered valid. Accordingly, if a funeral is brought to you and you do not know whether it is from the Muslims or not, say: “O Allah, if he was a believer, then forgive him and have mercy on him,” and Allah Blessed and Exalted is He knows that. And his saying to us, may Allah grant you success, is the saying of the Prophet (peace and blessings be upon him). Yes, what came. What, what, what did we return to? Look at what we returned to.