Sahih al-Bukhari 1598
Narrated Salim that his father said:
"Allah's Messenger (ﷺ), Usama bin Zaid, Bilal, and `Uthman bin abu Talha entered the Ka`ba and then 
closed its door. When they opened the door I was the first person to enter (the Ka`ba). I met Bilal and 
asked him, "Did Allah's Messenger (ﷺ) offer a prayer inside (the Ka`ba)?" Bilal replied in the affirmative and 
said, "(The Prophet (ﷺ) offered the prayer) in between the two right pillars."
حَدَّثَنَا قُتَيْبَةُ بْنُ سَعِيدٍ، حَدَّثَنَا اللَّيْثُ، عَنِ ابْنِ شِهَابٍ، عَنْ سَالِمٍ، عَنْ أَبِيهِ، أَنَّهُ قَالَ دَخَلَ رَسُولُ اللَّهِ صلى الله عليه وسلم الْبَيْتَ هُوَ وَأُسَامَةُ بْنُ زَيْدٍ، وَبِلاَلٌ، وَعُثْمَانُ بْنُ طَلْحَةَ، فَأَغْلَقُوا عَلَيْهِمْ فَلَمَّا فَتَحُوا، كُنْتُ أَوَّلَ مَنْ وَلَجَ، فَلَقِيتُ بِلاَلاً فَسَأَلْتُهُ هَلْ صَلَّى فِيهِ رَسُولُ اللَّهِ صلى الله عليه وسلم قَالَ نَعَمْ، بَيْنَ الْعَمُودَيْنِ الْيَمَانِيَيْنِ‏.‏