Al-Ghazālī wrote the Iḥyāʾ after a spiritual crisis led him to leave his professorship in Baghdad in 1095 and take up the Sufi path. In forty books it treats worship, social life, the vices and the virtues of the heart, making Sufi interiority central to mainstream Islam.
Iḥyāʾ ʿulūm al-dīn
The Revival of the Religious Sciences: al-Ghazālī’s great synthesis of law, ethics and Sufism.
Also: Revival of the Religious Sciences