Spiritual Retreat: Performing Iʿtikaf in One Mosque and Required Permission
Practical Laws of Islam as per the teachings of Ayatullah Sistani
Ruling 1729
It is necessary that iʿtikāf be performed in one mosque. Therefore, one iʿtikāf cannot be performed in two mosques, whether they are separate from each other or joined together, unless they are joined together in a manner that they are commonly considered one mosque.
viii. Iʿtikāf must be performed with the permission of one whose permission is legally (sharʿan) required.
vii. Iʿtikāf must take place in one mosque.
-Ayatullah Sistani, Practical Laws of Islam, Spiritual Retreat (Iʿtikāf)