Chapter on the Reasons Behind Hajj
Man Lā Yaḥḍuruh al-Faqīh|Volume 2|Book 3|Chapter 1
قَالَ اَلنَّبِيُّ صَلَّى اَللَّهُ عَلَيْهِ وَ آلِهِ: «سُمِّيَتِ اَلْكَعْبَةُ كَعْبَةً لِأَنَّهَا وَسَطُ اَلدُّنْيَا ».
The Prophet (peace and blessings be upon him and his family) said: "The Ka'bah was named 'Ka'bah' because it is the center of the world."
- Ṣaḥīḥ al-Faqīh