Why is the grave of the Messenger (peace be upon him) inside his mosque?

Question:
This is a message received from a group of young men who have a set of questions. The first question—Your Eminence, the Shaykh—says: What is the ruling on praying in a mosque that contains a grave? And why did the grave of the Messenger (peace and blessings be upon him) end up inside his mosque? We ask for guidance on this matter, and may you be rewarded.

Answer:
Prayer in mosques that contain graves is not valid and is not permissible. It is not permissible to bury people in mosques; rather, this is a practice of the Jews and the Christians. The Messenger (peace and blessings be upon him) cursed them for this practice, saying: .
It is obligatory for the people of Islam to beware of imitating them and to ensure that their graves are outside their mosques, in dedicated cemeteries. As for the mosque, it is not permissible to bury people in it, nor is it permissible to pray in a mosque that contains graves. This is because the presence of a grave in a mosque is a means to shirk (associating partners with Allah) and a means to calling upon others besides Allah and seeking aid from them. Therefore, it is not permissible for Muslims to bury their dead in mosques. Rather, it is obligatory for Muslims to bury their dead outside the mosques, in dedicated cemeteries, as the Prophet (peace and blessings be upon him) did in Madinah. He used to bury them in al-Baqi', and the martyrs were buried at the place where they were killed, at Uhud.
As for his grave (peace and blessings be upon him), it is in his house, not in the mosque. The Companions buried him in the house of 'A'ishah, fearing that excessive veneration would be shown to it if it were exposed in al-Baqi'. So they buried him in his house, out of concern that excessive veneration would occur and that his grave would be turned into a mosque. They buried him in the house. Then, when the mosque was expanded, it was included in the mosque—the house itself, the chamber—when al-Walid ibn 'Abd al-Malik, the Commander of the Faithful in his time, expanded it at the beginning of the first century of the Hijrah. He included the chamber—the chamber of the Prophet (peace and blessings be upon him)—in the mosque. 'A'ishah's chamber was included as part of it. The scholars of his time had advised him not to include it, but he saw that including it would not cause harm, because it is known that it is in his house, and the expansion called for it. He erred in this matter. May Allah forgive us, him, and every Muslim.
The point is that he (peace and blessings be upon him) was buried in his house, not in the mosque. The house was later included in the mosque, so it is now in his house, not in the mosque. It is not permissible to follow this example and say, "We will bury people in the mosque because of the grave of the Prophet (peace and blessings be upon him) in the mosque." No. The grave of the Prophet is in his house, in his house (peace and blessings be upon him), but the entire chamber was included in the mosque for the sake of the expansion.
It is obligatory for Muslims to beware of burying people in mosques and to obey the command of the Messenger (peace and blessings be upon him) regarding the prohibition of this. He (peace and blessings be upon him) said: . Therefore, people are not to be buried in mosques; rather, graves are to be outside the mosques. Mosques are prepared for prayer, worship, and recitation, so there should be no graves in them. Yes.