الاعتكاف مستحب، وهو اللبث في المسجد مع الصوم، ونية الاعتكاف.
Translation: Iʿtikāf is recommended; it consists of remaining in the mosque with fasting and the intention of iʿtikāf.
Lubth denotes staying in a place. Ordinary presence inside a mosque is not the same as devotional retreat; intention makes that stay an act of worship.