The World Federation One Stop Fiqh

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. And 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.