Sahih Muslim
Sahih Muslim 1331
It is recommended for pilgrims and others to enter the Ka'bah and pray therein, and supplicate in all its corners
Arabic hadith text
حَدَّثَنَا شَيْبَانُ بْنُ فَرُّوخَ، حَدَّثَنَا هَمَّامٌ، حَدَّثَنَا عَطَاءٌ، عَنِ ابْنِ عَبَّاسٍ، أَنَّ النَّبِيَّ صلى الله عليه وسلمدَخَلَ الْكَعْبَةَ وَفِيهَا سِتُّ سَوَارٍ فَقَامَ عِنْدَ سَارِيَةٍ فَدَعَا وَلَمْ يُصَلِّ
Translation
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.