Who are Ahlebayt??

Ibn Hajar Asqalani explain the meaning of “al-Bayt”

وفي ذكر البيت معنى اخر لان مرجع أهل بيت النبي صلى الله عليه و سلم إليها لما ثبت في تفسير قوله تعالى انما يريد الله ليذهب عنكم الرجس أهل البيت قالت أم سلمة لما نزلت دعا النبي صلى الله عليه و سلم فاطمة وعليا والحسن والحسين فجللهم بكساء فقال اللهم هؤلاء أهل بيتي الحديث أخرجه الترمذي وغيره ومرجع أهل البيت هؤلاء إلى خديجة لان الحسنين من فاطمة وفاطمة بنتها وعلي نشا في بيت خديجة وهو صغير ثم تزوج بنتها بعدها فظهر رجوع أهل البيت النبوي إلى خديجة دون غيرها

The word house (al-bayt) has a different meaning to it, because the household progeny of the prophet is from her (Khadija  ). Because it is proven in the explanation of the Holy Quran verse 33:33. “Allah only desires to take away any uncleanliness from you, O people of the household, and purify you (thorough purifying)”. Umm Salama says: “When this verse came down the Prophet called upon Fatimah, Ali, Hasan and Hussain and placed them under the cloak and said: O Allah, these are my Ahlubait.” Narrated by al-Tirmidhi and others, and these 4 members the ahl al-bayt are from Khadijah. Because the Hasanain (Hasan and Hussain) are from Fatimah, and Fatimah is the daughter of Khadijah, and Ali grew up in the house of Khadijah and later on he married her daughter therefore it is made evident the Prophet’s household progeny is from Khadijah and not from any of the others.

Source: Fathul-Bari,Vol 7,Pg 138