الِاعْتِكَافُ مُسْتَحَبٌّ، وَهُوَ اللُّبْثُ فِي الْمَسْجِدِ
Translation: Iʿtikāf is recommended, and it is remaining in the mosque.
Al-iʿtikāf is the first subject and mustaḥabb its predicate. Huwa begins the second nominal clause, with al-lubth as its predicate. Fī al-masjid specifies the place of remaining.