Why is the "crescent moon and star" being used as the symbol of Islam by some Muslims?

The use of the crescent moon and star as a symbol of Islam can be traced back to various historical and cultural factors rather than any direct religious mandate. The crescent moon is mentioned in the Qur'an in the context of timekeeping and religious observance, particularly concerning the lunar calendar which is central to Islamic practice.

In Surah Al-Baqara, it is stated: They ask thee, (O Muhammad), of new moons, say: They are fixed seasons for mankind and for the pilgrimage. It is not righteousness that ye go to houses by the backs thereof (as do the idolaters at certain seasons), but the righteous man is he who wardeth off (evil). So go to houses by the gates thereof, and observe your duty to Allah, that ye may be successful. 2:189. This verse indicates that the appearance of the crescent moon serves as a timekeeping mechanism for important events, particularly for the pilgrimage (Hajj) and fasting during Ramadan.

Historically, the crescent moon was a symbol used by various civilizations, and it became associated with Islam during the Ottomans, who adopted it as a symbol for their empire. Over time, the crescent moon and star became emblematic of Islamic identity, particularly in regions influenced by Ottoman culture.

Thus, while the crescent moon and star are not religious symbols in the Qur'an, their adoption in Islamic culture has historical roots that reflect the lunar calendar's significance in Islamic practices and the influence of historical empires.