Sahih Muslim 1331
Sahih Muslim · Book 15: The Book of Pilgrimage · It is recommended for pilgrims and others to enter the Ka'bah and pray therein, and supplicate in all its corners
حَدَّثَنَا شَيْبَانُ بْنُ فَرُّوخَ ، حَدَّثَنَا هَمَّامٌ ، حَدَّثَنَا عَطَاءٌ ، عَنِ ابْنِ عَبَّاسٍ ، أَنَّ النَّبِيَّ صلى الله عليه وسلم دَخَلَ الْكَعْبَةَ وَفِيهَا سِتُّ سَوَارٍ فَقَامَ عِنْدَ سَارِيَةٍ فَدَعَا وَلَمْ يُصَلِّ .
Ibn Abbas (Allah be pleased with them) reported that Allah's Apostle (ﷺ) entered the Ka'ba, and in it there were six pillars, and he stood near a pillar and made supplication, but did not observe the prayer.