Spiritual Retreat: Leaving the Place of Iʿtikaf to Perform Ghusl
Practical Laws of Islam as per the teachings of Ayatullah Sistani
Ruling 1746
If it becomes obligatory for a muʿtakif to perform ghusl, in case the ghusl is one of the ghusls that is not permitted to be performed in a mosque – such as the ghusl for janābah, which would require staying in the mosque while in the state of janābah or would cause the mosque to become impure – then he must leave; otherwise, his iʿtikāf becomes invalid. In case there is no problem in performing ghusl in the mosque – such as the ghusl for touching a corpse (mass al‑mayyit) – and it is possible to perform ghusl, then based on obligatory precaution, it is not permitted to leave the mosque.
-Ayatullah Sistani, Practical Laws of Islam, Spiritual Retreat (Iʿtikāf)