Sahih al-Bukhari 506
صحيح البخاري#506SahihNarrated Nafi':Whenever 'Abdullah entered the Ka'bah, he used to go ahead leaving the door of the Ka'bah behind him. He would proceed on till the remaining distance between him and the opposite wall was about three cubits. Then he would offer prayer there where the Prophet (ﷺ) had offered Salat, as Bilal informed me. Ibn 'Umar said, "It does not matter for any of us to offer prayers at any place inside the Ka'bah
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Every narration in Sahih al-Bukhari is accepted as Sahih (authentic) by the established status of the book.
In-book reference: 8:153