The Muslim holy month of Ramadan will begin Friday in Saudi Arabia, the birthplace of Islam, and most other Gulf Arab states.
Senior clerics made the decision after failing to spot a new moon on Wednesday. They said the four weeks of dawn-to-dusk fasting for Ramadan will begin Friday.
Muslims scan the sky at night in search of the new crescent moon that marks the beginning of the Islamic month. The timing often varies from country to country.
The world's most populous Muslim-dominated nation, Indonesia, also will start Ramadan on Friday. Muslims in Bangladesh, Pakistan and India will begin the fast on Saturday.
Fasting the month of Ramadan is one of Islam's five pillars, including the belief in one God and all His Prophets and Scriptures, especially the laws revealed to Moses, David, Jesus and Mohammed.
During the holy month, Muslims are forbidden to eat, drink or smoke during daylight hours. Followers traditionally end each day of fasting with feasts and visits to friends after sundown.
Also in Ramadan, the ninth lunar month of the Islamic calendar, Muslims around the world take a step back from their daily routines and focus on community, charity and prayer.