Al-Ghazali: The Mysteries of Charity and The Mysteries of Fasting. 
Book 5 and 6 of the Ihya ulum al-din

Abu Hamid Al-Ghazali

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-Ghazali 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.

In book 5 al-Ghazali begins with a discussion of the various kinds of zakāt and the conditions under which they become obligatory. He explains the manners related to zakat and its inward and outward conditions. He then discusses the recipients of zakat, who qualifies for it and in what circumstances, and the manners related to receiving it. Finally, al-Ghazali explains charity and its virtues.

In book 6 al-Ghazali begins with the outward obligations and sunnah elements of fasting, and what is required if the fast is broken. He explains the mysteries of fasting and its inner conditions. Finally, he discusses the voluntary fasts and their order in supererogatory worship.

This readable yet comprehensive work covers an array of issues from the essential outward aspects of paying charity, to the inward aspects of the state of the heart during the fast and how to humble oneself completely. As a practical, yet profound book, it is an indispensable guide for Muslims who seek a deeper comprehension of these two fundamental practices for Muslims, and for all those interested in understanding the meaning and role of charity and fasting in Islam.