The Quran says the new moons are "measurements of time for the people and for Hajj", and that Allah fixed twelve months from the day He created the heavens and the earth, four of them sacred. The Prophet ﷺ tied fasting to sighting the crescent. A lunar year is about eleven days shorter than a solar one, so Ramadan moves through every season.
When people asked the Prophet ﷺ about the new moons, Allah answered: "They are measurements of time for the
people and for Hajj" 1. The moon's phases were set so "that you may know the number of years and account [of
time]" 2. Anyone, anywhere, can look up and read this calendar, with no technology needed.
Allah also fixed the number of months: "the number of months with Allah is twelve [lunar] months in the
register of Allah [from] the day He created the heavens and the earth; of these, four are sacred" 3. The
Prophet ﷺ said time had returned to its original state, the year is twelve months, and he
named the four sacred months: Dhul-Qa'dah, Dhul-Hijjah, Muharram and Rajab 4. The pre-Islamic Arabs used to
postpone sacred months to suit themselves, and the Quran condemned this 5.
For worship, the crescent decides. "Whoever sights [the new moon of] the month, let him fast it" 6. The
Prophet ﷺ said: start fasting on seeing the crescent and stop on seeing it, and if it is cloudy, complete thirty
days 7. He also said a month is sometimes twenty-nine days and sometimes thirty 8.
One beautiful result: because the lunar year is shorter than the solar year, Ramadan and Hajj travel through
every season. Over a lifetime a Muslim fasts in long summer days and short winter days, and no region is
always favoured.
The evidence
1
Quran Al-Baqara · 2:189
The new moons are measurements of time for people and for Hajj.
They ask you, [O Muhammad], about the new moons. Say, "They are measurements of time for the people and for Hajj." And it is not righteousness to enter houses from the back, but righteousness is [in] one who fears Allah. And enter houses from their doors. And fear Allah that you may succeed
2
Quran Yunus · 10:5
The moon's phases let people know the number of years and the reckoning.
It is He who made the sun a shining light and the moon a derived light and determined for it phases - that you may know the number of years and account [of time]. Allah has not created this except in truth. He details the signs for a people who know
3
Quran At-Tawba · 9:36
Twelve months with Allah since the creation of the heavens and earth, four sacred.
Indeed, the number of months with Allah is twelve [lunar] months in the register of Allah [from] the day He created the heavens and the earth; of these, four are sacred. That is the correct religion, so do not wrong yourselves during them. And fight against the disbelievers collectively as they fight against you collectively. And know that Allah is with the righteous [who fear Him]
4
HadithSahih al-Bukhari 4662
SahihBukhari
Time has returned to its original state; twelve months, naming the four sacred ones.
Narrated Abu Bakr:The Prophet (ﷺ) said, "Time has come back to its original state which it had when Allah created the Heavens and the Earth; the year is twelve months, four of which are sacred. Three of them are in succession; Dhul-Qa'da, Dhul-Hijja and Al-Muharram, and (the fourth being) Rajab Mudar (named after the tribe of Mudar as they used to respect this month) which stands between Jumad (ath-thani) and Sha'ban
Indeed, the postponing [of restriction within sacred months] is an increase in disbelief by which those who have disbelieved are led [further] astray. They make it lawful one year and unlawful another year to correspond to the number made unlawful by Allah and [thus] make lawful what Allah has made unlawful. Made pleasing to them is the evil of their deeds; and Allah does not guide the disbelieving people
6
Quran Al-Baqara · 2:185
Whoever sights the month of Ramadan should fast it.
The month of Ramadhan [is that] in which was revealed the Qur'an, a guidance for the people and clear proofs of guidance and criterion. So whoever sights [the new moon of] the month, let him fast it; and whoever is ill or on a journey - then an equal number of other days. Allah intends for you ease and does not intend for you hardship and [wants] for you to complete the period and to glorify Allah for that [to] which He has guided you; and perhaps you will be grateful
7
HadithSahih al-Bukhari 1909
SahihBukhari
Fast on seeing the crescent, stop on seeing it; if cloudy, complete thirty days.
Narrated Abu Huraira:The Prophet (ﷺ) or Abul-Qasim said, "Start fasting on seeing the crescent (of Ramadan), and give up fasting on seeing the crescent (of Shawwal), and if the sky is overcast (and you cannot see it), complete thirty days of Sha'ban
العربية
حَدَّثَنَا آدَمُ، حَدَّثَنَا شُعْبَةُ، حَدَّثَنَا مُحَمَّدُ بْنُ زِيَادٍ، قَالَ سَمِعْتُ أَبَا هُرَيْرَةَ ـ رضى الله عنه ـ يَقُولُ قَالَ النَّبِيُّ صلى الله عليه وسلم أَوْ قَالَ قَالَ أَبُو الْقَاسِمِ صلى الله عليه وسلم " صُومُوا لِرُؤْيَتِهِ، وَأَفْطِرُوا لِرُؤْيَتِهِ، فَإِنْ غُبِّيَ عَلَيْكُمْ فَأَكْمِلُوا عِدَّةَ شَعْبَانَ ثَلاَثِينَ ".
8
HadithSahih al-Bukhari 1913
SahihBukhari
The month is sometimes twenty-nine and sometimes thirty days.
Narrated Ibn `Umar:The Prophet (ﷺ) said, "We are an illiterate nation; we neither write, nor know accounts. The month is like this and this, i.e. sometimes of 29 days and sometimes of thirty days
العربية
حَدَّثَنَا آدَمُ، حَدَّثَنَا شُعْبَةُ، حَدَّثَنَا الأَسْوَدُ بْنُ قَيْسٍ، حَدَّثَنَا سَعِيدُ بْنُ عَمْرٍو، أَنَّهُ سَمِعَ ابْنَ عُمَرَ ـ رضى الله عنهما ـ عَنِ النَّبِيِّ صلى الله عليه وسلم أَنَّهُ قَالَ " إِنَّا أُمَّةٌ أُمِّيَّةٌ، لاَ نَكْتُبُ وَلاَ نَحْسُبُ الشَّهْرُ هَكَذَا وَهَكَذَا ". يَعْنِي مَرَّةً تِسْعَةً وَعِشْرِينَ، وَمَرَّةً ثَلاَثِينَ.
This answer was compiled with the help of AI, using only the verified texts shown here. Every reference links to its source. If you find a mistake, please report it. Updated 2026-09-24