Hazrat Ibn Umar (may Allah be pleased with them both) asked Hazrat Bilal (may Allah be pleased with him), and he informed that the Noble Prophet (peace and blessings be upon him) prayed two rak'ahs inside the Ka'bah, keeping the pillar on his right side, moving a little forward, and keeping Maqam Ibrahim behind his back.
Hadith Referenceمسند احمد / مسند الأنصار رضي الله عنهم / 23905
Hadith Gradingحکم دارالسلام:حديث صحيح، خ: 397، م: 1329، وهذا إسناد حسن