Chapter on the Reasons Behind Hajj
Man Lā Yaḥḍuruh al-Faqīh|Volume 2|Book 3|Chapter 1
وَ حُرِّمَ اَلْمَسْجِدُ لِعِلَّةِ اَلْكَعْبَةِ وَ حُرِّمَ اَلْحَرَمُ لِعِلَّةِ اَلْمَسْجِدِ وَ وَجَبَ اَلْإِحْرَامُ لِعِلَّةِ اَلْحَرَمِ ».
"The mosque was made sacred because of the Kaaba, the sanctuary was made sacred because of the mosque, and Ihram became obligatory because of the sanctuary."
- Ṣaḥīḥ al-Faqīh