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 about three cubits. Then he would off 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."  

أَنَّ عَبْدَ اللَّهِ كَانَ إِذَا دَخَلَ الْكَعْبَةَ مَشَى قِبَلَ وَجْهِهِ حِينَ يَدْخُلُ وَجَعَلَ الْبَابَ قِبَلَ ظَهْرِهِ فَمَشَى حَتَّى يَكُونَ بَيْنَهُ وَبَيْنَ الْجِدَارِ الَّذِي قِبَلَ وَجْهِهِ قَرِيبًا مِنْ ثَلاَثَةِ أَذْرُعٍ صَلَّى يَتَوَخَّى الْمَكَانَ الَّذِي أَخْبَرَهُ بِهِ بِلاَلٌ أَنَّ النَّبِيَّ ﷺ صَلَّى فِيهِ قَالَ وَلَيْسَ عَلَى أَحَدِنَا بَأْسٌ إِنْ صَلَّى فِي أَىِّ نَوَاحِي الْبَيْتِ شَاءَ  

[Machine] He asked Bilal where did the Messenger of Allah ﷺ pray? Meaning, in the Kaaba. So Bilal showed him where he prayed, and he did not ask him how many prayers he performed. Ibn Umar, when he entered the house, would face its front and put the door behind his back, then he would walk until he was close to the wall, about the distance of three cubits, then he would pray, choosing the place that Bilal informed him that the Messenger of Allah ﷺ used to pray in.  

أَنَّهُ سَأَلَ بِلَالًا أَيْنَ صَلَّى رَسُولُ اللهِ ﷺ؟ يَعْنِي فِي الْكَعْبَةِ فَأَرَاهُ بِلَالٌ حَيْثُ صَلَّى وَلَمْ يَسْأَلْهُ كَمْ صَلَّى وَكَانَ ابْنُ عُمَرَ إِذَا دَخَلَ الْبَيْتَ مَشَى قِبَلَ وَجْهِهِ وَجَعَلَ الْبَابَ قِبَلَ ظَهْرِهِ ثُمَّ مَشَى حَتَّى يَكُونَ بَيْنَهُ وَبَيْنَ الْجِدَارِ قَرِيبٌ مِنْ ثَلَاثَةِ أَذْرُعٍ ثُمَّ صَلَّى يَتَوَخَّى الْمَكَانَ الَّذِي أَخْبَرَهُ بِلَالٌ أَنَّ رَسُولَ اللهِ ﷺ صَلَّى فِيهِ