assalam alaykum.i want clarification about why the two khalifahs of the prophet( peace be upon him)where buried with him in his house,as it is the khususiyya of the prophets to be buried where their soul are taken.i also learnt that it is not part of sunnah to bury the deads in building

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His Slave and Messenger.

First of all, we would like to mention that the majority of jurists are of the opinion that it is permissible to bury in houses while some of them hold that this is against what is most appropriate. Also, some other jurists hold that it is dislikeable.

Burying Abu Bakr and ‘Umar beside the Prophet, sallallaahu ‘alayhi wa sallam, in the room of ‘Aa’ishah does not contradict the special privilege of the Prophets that they are buried where they die. Had this contradicted that privilege, then they would never have done it. Abu Bakr instructed ‘Aa’ishah to be buried beside the Messenger of Allaah, sallallaahu ‘alayhi wa sallam, and ‘Umar sought her permission to be buried beside them. ‘Aa’ishah herself wanted to be buried beside them (the Prophet, sallallaahu ‘alayhi wa sallam, and Abu Bakr), but she preferred to let ‘Umar have this honor.

Furthermore, burying them besides the Prophet, sallallaahu ‘alayhi wa sallam, was an interpretation of an incident that occurred to them with the Messenger of Allaah, sallallaahu ‘alayhi wa sallam, when they were sitting beside him on the side of the well while ‘Uthmaan sat on the opposite side. Sa‘eed ibn Al-Musayyib said, "I interpret this (incident) in terms of their graves." [Al-Bukhari and Muslim]

An-Nawawi said in his explanation of Saheeh Muslim, commenting on that statement: "It means that the three (i.e. the Prophet, sallallaahu ‘alayhi wa sallam, Abu Bakr and ‘Umar) were buried in the same place while ‘Uthmaan was buried in a place away from them. This is a form of truthful insight." [End quote]

Allaah Knows best.