Suppose intercourse occurs after ifṭār at night. No daytime fast is then being observed, yet iʿtikāf is invalidated under the cited rule.
A question about the validity of fasting is legally separate. Every case should specify whether it is asking about the fast or the retreat.
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Bab al-Iʿtikaf: Rules, Restrictions, Invalidation and Vows
Suppose intercourse occurs after ifṭār at night. No daytime fast is then being observed, yet iʿtikāf is invalidated under the cited rule.
A question about the validity of fasting is legally separate. Every case should specify whether it is asking about the fast or the retreat.