Allah says in the Quran - And We have made the night and day two signs, and We erased the sign of the night and made the sign of the day visible that you may seek bounty from your Lord and may know the number of years and the account [of time]. And everything We have set out in detail. (Surah Al-Isra, 17:12)
The universal law that governs the succession of day and night is linked to numerous aspects of human life. It is linked with people’s efforts in earning their living, and their knowledge of time and calculation. It also relates to the good and evil man may earn in life and what reward he may achieve in the end for either his good or bad actions. Indeed the consequences of following guidance or error relate to it, as is the individual nature of responsibility which means that no one will have to answer for anyone else. The same universal law is linked to Allah’s promise that He (swt) will not inflict punishment on anyone until He (swt) has sent His messengers.
This link further applies to the law which governs the destruction of communities only after the affluent among them have been guilty of immense transgression. The law further relates to the diverse destinies of those who seek the pleasures of this world and those who prefer the good reward of the hereafter, and what Allah (swt) grants to both in this life and in the life to come. All these aspects follow a well set system and certain immutable laws besides. Nothing takes place haphazardly. Allah (swt) says -
وَجَعَلۡنَا الَّيۡلَ وَالنَّهَارَ اٰيَتَيۡنِ فَمَحَوۡنَاۤ اٰيَةَ الَّيۡلِ وَجَعَلۡنَاۤ اٰيَةَ النَّهَارِ مُبۡصِرَةً لِّتَبۡتَغُوۡا فَضۡلًا مِّنۡ رَّبِّكُمۡ وَلِتَعۡلَمُوۡا عَدَدَ السِّنِيۡنَ وَالۡحِسَابَؕ وَكُلَّ شَىۡءٍ فَصَّلۡنٰهُ تَفۡصِيۡلًا
“We have made the night and the day as two [of Our] signs. Then We have effaced the sign of the night while the sign of the day We have left enlightened, so that you may seek bounty from your Lord, and you may learn to compute the years and be able to reckon. Most clearly have We spelled out everything.” (Surah 17:12)
The night and the day are two major universal signs which confirm the accuracy of the law governing the universe which operates all the time, suffering neither a failure nor a temporary need for repairs. So what is meant here by ‘effacing the sign of the night’, when we see that this sign remains operative as much as the sign of the day? It seems to me, and Allah (swt) knows best, that the reference here is to the darkness of the night which hides everything and during which movement slows down. The darkness gives the impression that the night is effaced when compared with the day, its light and the bustling activity that takes place under its light. It is as though the day is able to see things by its light and reveals everything for us to behold. The effacing of the night and the full visibility of the day have a clearly specified purpose: “so that you may seek bounty from your Lord, and you may learn to compute the years and be able to reckon.” This makes things very clear: the night is for rest and recuperation, and the day for work, earning one’s living and activity. The succession of the day and night enables people to compute the years and determine the seasons and set times for different transactions. “Most clearly have We spelled out everything.” There is nothing in the universe that has been left to chance. The accuracy that is manifested in the succession of day and night confirms the elaborate and faultless design of everything Allah (swt) has created.
During the early days of Islam, muslims addressed the Prophet Muhammad (pbuh) with specific enquiries relating to a wide range of everyday issues and situations they were encountering in their new way of life. They reveal a genuine desire on the part of the new Muslims to find out what their new religion has to say about these matters. The believers wanted to learn more about how Islam viewed and interpreted the social and physical phenomena they were experiencing in the world around them. They ask about the moon and the various phases it goes through. Why does it start as a fine crescent which becomes bigger until it develops into a full sphere, and then reverses the cycle until it disappears altogether before it is reborn in the shape of a thin crescent again? Allah (swt) revealed the Quran as a blueprint for a complete way of life, a stimulus, a driving force guiding the Muslim community, charting its course through thick and thin, and helping it overcome and avoid all the difficulties and obstacles it is bound to encounter in this world. Allah (swt) mentioned in the Quran -
يَسۡـئَلُوۡنَكَ عَنِ الۡاَهِلَّةِ ؕ قُلۡ هِىَ مَوَاقِيۡتُ لِلنَّاسِ وَالۡحَجِّ ؕ
People question you concerning the phases of the moon. Say: “They are signs to determine time for the sake of people and for the Pilgrimage.” (Surah 2:189) The waxing and waning of the moon has attracted men's attentions throughout the ages and all kinds of fanciful ideas, superstitions and rituals have been, and are still today, associated with it. The moon was considered the basis of good and bad omens. Certain dates were considered auspicious and others inauspicious for starting journeys, for beginning new tasks, for weddings and so on on the ground that the rising and setting of the moon, its waxing and waning and its eclipse affect human destiny. The Arabs too had their share of such superstitions. It was therefore natural that enquiries regarding such matters should be addressed to the Prophet.
In response, Allah (swt) says that the waxing and waning of the moon is nothing more than a physical phenomenon. By its appearance in the firmament the moon enables man to divide his year and it can thus be considered nature's own calendar. Particular reference is made to Hajj because it occupied the position of highest importance in the religious, cultural and economic life of the Arabs.
The length of each month is determined by the duration of a Moon cycle or lunation, specifically the time from one waxing crescent moon to the next. `Abdullah bin `Umar (r.a) narrates that Allah's Messenger (ﷺ) said, "The month (can be) 29 nights (i.e. days), and do not fast till you see the moon, and if the sky is overcast, then complete Sha'ban as 30 days."
حَدَّثَنَا عَبْدُ اللَّهِ بْنُ مَسْلَمَةَ، حَدَّثَنَا مَالِكٌ، عَنْ عَبْدِ اللَّهِ بْنِ دِينَارٍ، عَنْ عَبْدِ اللَّهِ بْنِ عُمَرَ ـ رضى الله عنهما ـ أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم قَالَ " الشَّهْرُ تِسْعٌ وَعِشْرُونَ لَيْلَةً، فَلاَ تَصُومُوا حَتَّى تَرَوْهُ، فَإِنْ غُمَّ عَلَيْكُمْ فَأَكْمِلُوا الْعِدَّةَ ثَلاَثِينَ ".
Reference : Sahih al-Bukhari 1907; Book 30, Hadith 17; Vol. 3, Book 31, Hadith 131
Um Salama (r.a) also narrates that - The Prophet (ﷺ) vowed to keep aloof from his wives for a period of one month, and after the completion of 29 days he went either in the morning or in the afternoon to his wives. Someone said to him "You vowed that you would not go to your wives for one month." He replied, "The month is of 29 days."
حَدَّثَنَا أَبُو عَاصِمٍ، عَنِ ابْنِ جُرَيْجٍ، عَنْ يَحْيَى بْنِ عَبْدِ اللَّهِ بْنِ صَيْفِيٍّ، عَنْ عِكْرِمَةَ بْنِ عَبْدِ الرَّحْمَنِ، عَنْ أُمِّ سَلَمَةَ ـ رضى الله عنها ـ أَنَّ النَّبِيَّ صلى الله عليه وسلم آلَى مِنْ نِسَائِهِ شَهْرًا، فَلَمَّا مَضَى تِسْعَةٌ وَعِشْرُونَ يَوْمًا غَدَا أَوْ رَاحَ فَقِيلَ لَهُ إِنَّكَ حَلَفْتَ أَنْ لاَ تَدْخُلَ شَهْرًا. فَقَالَ " إِنَّ الشَّهْرَ يَكُونُ تِسْعَةً وَعِشْرِينَ يَوْمًا ".
Reference : Sahih al-Bukhari 1910; Book 30, Hadith 20; Vol. 3, Book 31, Hadith 134
In an another hadith, Narrated Rib'i b. Hirash: On the authority of a man from the Companions of the Prophet (ﷺ): People differed among themselves on the last day of Ramadan (about the appearance of the moon of Shawwal). Then two bedouins came and witnessed before the Prophet (ﷺ) swearing by Allah that they had sighted moon the previous evening. So the Messenger of Allah (ﷺ) commanded the people to break the fast. The narrator Khalaf has added in his version: "and that they should proceed to the place of prayer (for 'Id)". Grade: Sahih (Al-Albani)
حَدَّثَنَا مُسَدَّدٌ، وَخَلَفُ بْنُ هِشَامٍ الْمُقْرِئُ، قَالاَ حَدَّثَنَا أَبُو عَوَانَةَ، عَنْ مَنْصُورٍ، عَنْ رِبْعِيِّ بْنِ حِرَاشٍ، عَنْ رَجُلٍ، مِنْ أَصْحَابِ النَّبِيِّ صلى الله عليه وسلم قَالَ اخْتَلَفَ النَّاسُ فِي آخِرِ يَوْمٍ مِنْ رَمَضَانَ فَقَدِمَ أَعْرَابِيَّانِ فَشَهِدَا عِنْدَ رَسُولِ اللَّهِ صلى الله عليه وسلم بِاللَّهِ لأَهَلاَّ الْهِلاَلَ أَمْسِ عَشِيَّةً فَأَمَرَ رَسُولُ اللَّهِ صلى الله عليه وسلم النَّاسَ أَنْ يُفْطِرُوا زَادَ خَلَفٌ فِي حَدِيثِهِ وَأَنْ يَغْدُوا إِلَى مُصَلاَّهُمْ .
Reference : Sunan Abi Dawud 2339; Book 14, Hadith 27; Book 13, Hadith 2332
Enough evidence for us to understand, a month starts on witnessing of a new moon crescent and ends on Witnessing of moon on the night after completion of 29 days and if there is no true witness who has sighted the moon - the month ends on completion of 30 days.
Its a Personal Responsibility
The law of action and reward is directly linked to the meticulous law of the universe: Allah (swt) further says -
وَكُلَّ اِنۡسَانٍ اَلۡزَمۡنٰهُ طٰۤـئِرَهٗ فِىۡ عُنُقِهٖؕ وَنُخۡرِجُ لَهٗ يَوۡمَ الۡقِيٰمَةِ كِتٰبًا يَّلۡقٰٮهُ مَنۡشُوۡرًا اِقۡرَاۡ كِتٰبَك َؕ كَفٰى بِنَفۡسِكَ الۡيَوۡمَ عَلَيۡكَ حَسِيۡبًا ؕ
Every human being’s action have We tied around his own neck. On the Day of Resurrection We shall produce for him a record which he will find wide open. [And We will say:] ‘Read this your record! Sufficient it is for you today that your own soul should make out your account.’ (Surah 17:13-14) “We have fastened his fate to his neck”: therefore one does not need to take omens from a bird. This is to remove the superstition of the disbelievers who used to take omens from birds etc. as if to say: The causes and consequences of good fortune or bad fate exist in man’s own person. He merits good fortune because of his own good conduct and good judgment, and likewise, suffers the consequences of evil fate by the lack of these. This was necessitated because foolish people always try to attribute their misfortunes to external causes, when in fact our fate depends on our own deeds, good or bad. If they probe into the causes, they will find that their fate was decided by their own good or bad qualities and judgments.
Rest Allah knows best.
Source: Quran, Tafseer Ibn Kathir, In the shade of the Quran, Hadith