In the Mysteries of Charity and Its Important Elements (Kitāb asrār al‑zakāt wa-muhimātiha;book 5), and the Mysteries of Fasting and Its Important Elements (Kitāb asrār al-ṣiyyām wa-muhimātiha; book 6), of the forty books of the Revival of the Religious Sciences (Iḥyāʾ ʿulūm al-dīn), Abū Ḥāmid al-Ghazālī explains the inner and outer meanings of charity and fasting, two pillars of worship for Muslims. These are two of the five books that deal with the inner dimensions of Islamic worship; books 3, 4, and 7 address purification, prayer, and pilgrimage, respectively.