When should Muslims start fasting in Ramadan?
`Abd-Allah ibn `Umar narrated that the Messenger of Allah (peace and blessings of Allah be upon him) spoke of Ramadan and said: “Do not fast until you see the new moon, and do not break the fast until you see it, and if it is covered then complete the month.” (Narrated by al-Bukhaari, 1906; Muslim, 1080)
This hadith indicates that it is obligatory to fast Ramadan when the sighting of the new moon is confirmed according to Shari`ah. It also indicates that it is obligatory to break the fast when it is confirmed that the new moon of Shawwal has been sighted according to Shari`ah.
It is also obligatory to complete Sha`ban as thirty days if clouds prevent sighting of the new moon of Ramadan, and it is obligatory to complete Ramadan as thirty days if clouds prevent sighting of the new moon of Shawwal. The basic principle is that the month continues and it not judged to have ended until there is certainty. It is not essential for each person to sight the moon for himself, rather if it is sighted by someone whose testimony that the month has begun or ended is acceptable, then the ruling applies.
The words “if it is covered” means if the new moon is concealed and covered by clouds etc.
“Then complete the month” means make it thirty days. This meaning is confirmed by the words narrated in al-Saheehayn: “If it (the new moon) is covered then complete the number (of days) as thirty.”
Can you fast the Day of Doubt?
The day of doubt is the night of the thirtieth of Sha`ban [in the Islamic calendar days are regarded as starting at sundown], if the new moon is not sighted or is covered with clouds etc.
It is not permissible to fast on the day of doubt because the Messenger of Allah (peace and blessings of Allah be upon him) commanded the Muslims to complete Sha`ban as thirty days if the new moon was concealed, because that night is part of Sha`ban unless there is certain evidence that it is Ramadan.
`Ammaar ibn Yaasir (may Allah be pleased with him) said: “Whoever fasts the day concerning which there is doubt has disobeyed Abu’l-Qaasim (peace and blessings of Allah be upon him).” (Narrated by al-Tirmidhi, 686; al-Nasaa’i, 2188; classed as saheeh by al-Albaani in Saheeh al-Tirmidhi, 553)
We should also pay attention to the new moon of Sha`ban so that we can watch out for the thirtieth night and seek the new moon of Ramadan.
The month should be completed if the new moon is not sighted. Abu Hurayrah (may Allah be pleased with him) said: The Messenger of Allah (peace and blessings of Allah be upon him) said: “Follow the progress of the moon through Sha`ban so that you may seek Ramadan.” (Narrated by al-Tirmidhi, 687; classed as hasan by al-Albaani in al-Silsilah al-Saheehah, 565)
What this hadith means is: try to work out when Sha`ban will begin and strive to watch the phases of the moon so that you will be ready to watch out for the new moon of Ramadan and you will not miss any of it.