Spiritual Retreat: Sitting on a Usurped Carpet or Taking a Reserved Place

Practical Laws of Islam as per the teachings of Ayatullah Sistani

Ruling 1761

If a muʿtakif sits on a usurped (ghaṣbī) carpet and he is aware of the fact that it is usurped, he commits a sin but his iʿtikāf does not become invalid. If someone gets to a place first and reserves it and a muʿtakif takes his place without his consent, then although he commits a sin, his iʿtikāf is valid.

-Ayatullah Sistani, Practical Laws of Islam, Spiritual Retreat (Iʿtikāf)