Voluntary Fasting in Islam
Question

I would like to learn the exact time for iftar and sahur, how many days in a month one should fast, exactly which day of the week it is supposed to be as well. Please provide me with as much as you can details about that.
Praise be to Allah.By His Wisdom, Allah has prescribed that His slaves should voluntarily seek to draw closer to Him, after performing the obligatory acts of worship, by doing more of the same kinds of acts of worship, and He has assigned to that great rewards, as the Prophet (peace and blessings of Allah be upon him) told us that his Lord said: “My slave does not draw near to Me with anything more beloved to Me than the religious duties I have enjoined upon him, and My slave continues to draw near to Me with supererogatory works so that I will love him, When I love him, I am his hearing with which he hears, his seeing with which he sees, his hand with which he strikes and his foot with which he walks. Were he to ask [something] of Me, I would surely give it to him, and were he to ask Me for refuge, I would surely grant him it.” (al-Bukhari, 6502) 
Types of voluntary fasting
Nafl fasts fall into two main categories: 

General voluntary fasts (i.e., not restricted to any particular time or circumstances). The Muslim may observe a voluntary fast on any day of the year that he wishes, except those which are known to be forbidden, such as the two ‘Eid days, on which fasting is haram, and Ayyam al-Tashriq (the three days following ‘Eid al-Adha), on which fasting is haram except on Hajj for those who do not have a hadiy (animal for sacrifice). Also excluded is deliberately singling out Friday for fasting, because it was reported that this is not allowed. One of the best forms of voluntary fasting is to fast alternate days for those who are able to do that, as it says in the hadith: “The most beloved prayer to Allah is the prayer of Dawud (peace be upon him), and the most beloved fasting to Allah is the fasting of Dawud. He used to sleep half the night, stand in prayer for one-third of the night, and sleep for one-sixth, and he used to fast alternate days.” (al-Bukhari, 1131; Muslim, 1159) 

In order for this kind of fasting to be regarded as virtuous, it should not weaken a person and make him unable to do his primary duties, as it says in the hadith: “he used to fast alternate days, and he never ran away from battle (because he used to break his fast at times of jihad).” (al-Bukhari, 1977; Muslim, 1159) 

Specific voluntary fasts. These are superior to general voluntary fasts, and are of two types: 

Types of Specific voluntary fasts

The first type is fasts which are specific to a type of person, such as young men who cannot get married, as mentioned in the hadith of ‘Abd-Allah ibn Mas’ud (may Allah be pleased with him): “We were young men with the Prophet (peace and blessings of Allah be upon him) and we did not have anything (i.e., we could not afford to get married). The Messenger of Allah (peace and blessings of Allah be upon him) said to us, ‘O young men, whoever among you can afford to get married, then let him do so, for it is more effective in lowering the gaze and guarding chastity. And whoever is not able to do that, then let him fast, for that will be a shield for him.’” (al-Bukhari, 5066; Muslim, 1400) 

This kind of fasting is more emphasized so long as a person is single, and this prescription is more emphatic the more provocation there is. There is no mention of any specific number of days in this case. 

The second type is fasts prescribed at specific times, which vary, with some being weekly, some monthly and some annual. 


The weekly fasts are on Monday and Thursday , on which days fasting is mustahabb. It was narrated that ‘Aishah said: “The Messenger of Allah (peace and blessings of Allah be upon him) was keen to fast on Mondays and Thursdays.” (al-Nasai, 2320; classed as sahih by al-Albani in Sahih al-Jami’ al-Saghir, 4827). 

The Prophet (peace and blessings of Allah be upon him) was asked about fasting on Mondays and Thursdays, and he said: “Those are two days on which people’s deeds are shown to the Lord of the Worlds, and I want my deeds to be shown to Him when I am fasting.” (Al-Nasai, 2358; Ibn Majah, 1740; Ahmad, 8161; classed as sahih by al-Albani in Sahih al-Jami’, 1583). He was asked about fasting on Mondays and he said, “On that day I was born and on that day revelation came to me.” (Muslim, 1162) 

With regard to the monthly fasts, it is mustahabb to fast on three days of each month. It was narrated that Abu Hurayrah (may Allah be pleased with him) said: “My close friend [i.e., the Prophet (peace and blessings of Allah be upon him)] advised me to do three things which I will never give up until I die: fasting three days each month, praying Duha, and sleeping after praying Witr.” (al-Bukhari, 1178; Muslim, 721). It is mustahabb to observe this fast in the middle of the hijri month, on the days called Ayyam al-Bid . 

It was narrated that Abu Dharr said: “The Messenger of Allah (peace and blessings of Allah be upon him) said to me, ‘If you fast any part of the month then fast on the thirteenth, fourteenth and fifteenth.’” (al-Nasai, 2424; Ibn Majah, 1707; Ahmad, 210; classed as sahih by al-Albani in Sahih al-Jami’ al-Saghir, 673) 

Annual fasts are observed on specific days, or during periods when it is Sunnah to fast. 

Sunnah days to fast
The specific days include the following: 

The day of `Ashura which is the tenth of al-Muharram . It was narrated that Ibn 'Abbas (may Allah be pleased with him) was asked about fasting on the day of `Ashura. He said, “I do not know of any day on the Messenger of Allah (peace and blessings of Allah be upon him) fasted that was better than this day and any month that was better than this month, meaning Ramadan.” (al-Bukhari, 2006; Muslim, 1132). It is Sunnah to fast the day before or the day after along with `Ashura, in order to be different from the Jews.
The day of `Arafah , which is the ninth day of Dhu’l-Hijjah. It is mustahabb only for those who are not standing in `Arafah itself, as the Messenger of Allah (peace and blessings of Allah be upon him) said concerning the virtue of the three fasts mentioned above: “The observance of three days' fast every month and that of Ramadan every year is equivalent to fasting for the entire year. I seek from Allah that fasting on the day of `Arafah may atone for the sins of the preceding and the coming years, and I seek from Allah that fasting on the day of `Ashura may atone for the sins of the preceding year.” (Muslim, 1162). 

Periods when it is Sunnah to fast
The periods during which it is Sunnah to fast include the following: 

The month of Shawwal . It is Sunnah to fast six days of Shawwal, because the Messenger of Allah (peace and blessings of Allah be upon him) said: “Whoever fasts Ramadan then fasts six days of Shawwal, it is as if he fasted for a lifetime.” (Muslim, 1164).
The month of Muharram: it is Sunnah to fast whatever one can of this month, because of the hadith: “The best of fasting after Ramadan is the month of Allah al-Muharram, and the best of prayer after the obligatory prayers is prayer at night (qiyam al-layl).” (Muslim, 1163)
The month of Sha`ban, as it was narrated that ‘Aishah (may Allah be pleased with her) said: “The Messenger of Allah (peace and blessings of Allah be upon him) used to fast until we thought that he would never break his fast, and he would not fast until we thought that he would never fast. I never saw the Messenger of Allah (peace and blessings of Allah be upon him) fast an entire month apart from Ramadan, and the month in which I saw him fast the most was Sha’ban. He used to fast all of Sha`ban or all of it apart from a few days.”  (al-Bukhari, 1969; Muslim, 1156) 

The Muslim who is keen to do good must realize the great virtue of performing voluntary fasts for the sake of Allah, as it says in the hadith of the Prophet (peace and blessings of Allah be upon him): “Whoever fasts one day for the sake of Allah, Allah will keep his face seventy years’ distance from Hell,” (al-Nasai, 2247; classed as sahih by al-Albani in Sahih Sunan al-Nasai, 2121)
We ask Allah to make us among those whose faces He keeps far away from Hell and its heat, and to bless us with Paradise. 
Precise timing of Suhur and Iftar
With regard to the precise timing of Suhur and Iftar:
As mentioned in the definition of fasting, fasting means abstaining from food, drink and all other things that break the fast from dawn until sunset, as Allah says (interpretation of the meaning): 
“and eat and drink until the white thread (light) of dawn appears to you distinct from the black thread (darkness of night), then complete your Sawm (fast) till the nightfall” [Al-Baqarah 2:187]
So the fasting person must begin to abstain from things that break the fast when dawn begins and continue until the sun has set. 
The Messenger of Allah (peace and blessings of Allah be upon him) said concerning the time of iftar: “When the night has come from here and the day has gone from here, and the sun has set, then let the fasting person break his fast.” (al-Bukhari, 1818; Muslim, 1841). 
With regard to the time of suhur, the majority of jurists said that it is the time from the last half of the night until the second dawn. It is Sunnah to delay it, according to the majority of scholars, so long as the second dawn has not begun, because of the verse quoted above and because the Prophet (peace and blessings of Allah be upon him) said: “Hasten iftar and delay suhur.” (Narrated by al-Tabarani and classed as sahih by al-Albani in Sahih al-Jami’, 3989).
The purpose of suhur is to give one strength to fast, so the closer it is to dawn the more effective it will be in helping one to fast. We ask Allah to make us among those who adhere to His laws and act according to them. May Allah send blessings and peace upon our Prophet Muhammad.
And Allah knows best.