Which of the following is NOT one of the pillars of Islam?

Monastic living is indeed not one of the pillars of Islam. The pillars of Islam consist of the core beliefs and practices that are central to the faith, which include the Shahada (the statement of faith), the five daily prayers (Salah), giving to charity (Zakat), fasting during Ramadan (Sawm), and the pilgrimage to Mecca (Hajj).

In contrast, monastic living is primarily associated with certain branches of Christianity, where individuals may take vows of celibacy and separation from society to devote themselves to spiritual practice. This concept does not align with Islamic teachings, which emphasize community, interaction with society, and fulfilling one's religious duties in everyday life rather than retreating from the secular world. Thus, identifying monastic living as not part of the pillars of Islam is accurate.