Fasting Mondays and Thursday
Most of the evidence about the voluntary fasting in Islam comes from the Sunnah of the Prophet SAW, as the references in the Qu'ran refer mainly to the obligation of fasting Ramadan on the Believer. The Qu'ran does give us some insight into the importance of fasting, in the English interpretation,
"O you who believe! Observing As-Sawm is prescribed for you as it was prescribed for those before you, that you may become Al-Muttaqun (the pious)." [Chapter 2: Verse 183].
It is clear from this that fasting it an integral part of becoming a pious Muslim, a true Believer in Allah SWT.
Also
“For Muslim men and women, for believing men and women, for devout men and women, for true men and women, for men and women who are patient and constant, for men and women who humble themselves, for men and women who give in Charity, for men and women who fast (and deny themselves), for men and women who guard their chastity, and for men and women who engage much in Allah’s praise - for them has Allah prepared forgiveness and great reward.” (Chapter 33, Verse 35)
So we can see again that fasting is an integral part of being a devout Muslim and that it is a part of obtaining the forgiveness of Allah SWT and His rewards.
While many other aspects of worship have had their reward defined in the Qu'ran and Sunnah, fasting is something that is done only for Allah SWT and the reward will not be know by the Believer until the Day of Judgement.
Abu Huraira (Allah be pleased with him) reported Allah's Messenger (may peace be upon him) said: Every (good) deed of the son of Adam would be multiplied, a good deed receiving a tenfold to seven hundredfold reward. Allah, the Exalted and Majestic, has said: With the exception of fasting, for it is done for Me and I will give a reward for it, for one abandons his passion and food for My sake. There are two occasions of joy for one who fasts, joy when he breaks it, and joy when he meets his Lord, and the breath (of an observer of fast) is sweeter to Allah than the fragrance of musk. Muslim and similar version in Maliks Muwatta
Fasting has a unique attribute that no other form of worship has, it is done entirely for Allah SWT.
There is also greater benefit in making voluntary fast a regular habit as narrated by
'A'isha (Allah be pleased with her) reported: The Messenger of Allah (may peace be upon him) did not observe fast in any month of the year more than in the month of Sha'ban, and used to say: Do as many deeds as you are capable of doing, for Allah will not become weary (of giving you reward), but you would be tired (of doing good deeds); and he also said: The deed liked most by Allah is one to which the doer adheres constantly even if it is small. Muslim+Bukhari
So there is evidence that it if preferable to take on a small number of extra good deeds, or in this case fasts, and hold steadfast in the good deed than to take on more than you can manage and stop doing the voluntary fasts at all.
We have gone over the punishments of the Hellfire and the rewards of Paradise. Insha Allah after understanding these great trials and rewards from Allah SWT we are keen to find ways to protect ourselves from those torments and tortures and earn ourselves the great rewards and delights.
Fasting is a source of protection from the Fire, as Ahmad reports from Jaabir ibn 'Abdullah:
"The Prophet (saw) said, "Allah (swt) says, "Fasting is a shield with which one may protect oneself from the Fire". (Sahih al-Jami, 4/114)
And also as reported by Abu Sa'id al Khudri (Allah be pleased with him) reported Allah's Messenger (may peace be upon him) as saying: Every servant of Allah who observes fast for a day in the way of Allah, Allah would remove, because of this day, his face farther from the Fire (of Hell) to the extent of seventy years' distance. Muslim
So each day of fasting will take your face 70 years distance from the hellfire. Next time you are sitting close to the open fire and you feel the heat of it on your face, remember this hadeeth, the heat of the Hellfire is 70 times hotter than any fire on this earth. Surely a day of fasting is worth this result.
The fast will also intercede on the behalf of a Believer, 'Abdullah ibn 'Amr reported that the Messenger of Allah, upon whom be peace, said: "The fast and the Qur'an are two intercessors for the servant of Allah on the Day of Resurrection. The fast will say: 'O Lord, I prevented him from his food and desires during the day. Let me intercede for him.' The Qur'an will say: 'I prevented him from sleeping at night. Let me intercede for him.' And their intercession will be accepted." Ahmad related this hadith with a sahih chain.
There is a special gate for the believers who fasted to enter Paradise,
In this hadeeth narrated by Sahl b. Sa'd (Allah be pleased with him) reported Allah's Messenger (may peace be upon him) as saying: In Paradise there is a gate which is called Rayyan through which only the observers of fast would enter on the Day on Resurrection. None else would enter along with them. It would be proclaimed: Where are the observers of fast that they should be admitted into it?-and when the last of them would enter, it would be closed and no one would enter it. Muslim
So there will be a gate especially for the fasting believers. The Prophet SAW also emphasised the importance that fasting has on entering Paradise. Abu Umamah reported: "I came to the Messenger of Allah and said: 'Order me to do a deed that will allow me to enter Paradise.' He said: 'Stick to fasting, as there is no equivalent to it.' Then I came to him again and he said: 'Stick to fasting."' This hadith is related by Ahmad, an-Nasa'i, and al-Hakim who classified it as sahih.
Allah SWT will reward those who fast , not just with a special gate to enter Paradise but with special dwelling in the Hereafter, "In Paradise there are dwellings whose inside can be seen from the outside, and the outside can be seen from inside. Allaah [swt] has prepared them for those who feed the hungry, and speak softly and gently, fast continuously and pray at night whilst the people are asleep." Saheeh al-Jami'
There are other benefits of fasting voluntary fast that we can attain before the Day of Judgement and before entering the next life.
There are times in our lives where we need help in controlling our own desires. Infact for the honest person I would say all of our lives since we are all assigned a Jinn that will tempt us away until our soul is removed from our body as confirmed in Sahih Muslim, narrated Abdullah ibn Mas'ud, similar a narration by 'Aisha, r.a. Allah's Apostle said: There is none amongst you with whom is not an attached from amongst the jinn (devil). They (the Companions) said: Allah's Apostle with you too? Thereupon he said: Yes, but Allah helps me against him and so I am safe from his hand and he does not command me but for good.’
Fasting is known to be the advice of the Prophet SAW for the controlling of desires.
Narrated 'Alqama: While I was walking with 'Abdullah he said, "We were in the company of the Prophet and he said, 'He who can afford to marry should marry, because it will help him refrain from looking at other women, and save his private parts from looking at other women, and save his private parts from committing illegal sexual relation; and he who cannot afford to marry is advised to fast, as fasting will diminish his sexual power." Bukhari
For those who are fortunate enough to be married and not suffer this, there are other aspects of fasting that help us control ourselves in this life. As reported by Narrated Abu Huraira:
The Prophet said, "Whoever does not give up forged speech and evil actions, Allah is not in need of his leaving his food and drink (i.e. Allah will not accept his fasting.)" Bukhari
And in another hadeeth also reported by Abu Huraira: Allah's Apostle said, "Fasting is a shield (or a screen or a shelter). So, the person observing fasting should avoid sexual relation with his wife and should not behave foolishly and impudently, and if somebody fights with him or abuses him, he should tell him twice, 'I am fasting." The Prophet added, "By Him in Whose Hands my soul is, the smell coming out from the mouth of a fasting person is better in the sight of Allah than the smell of musk. (Allah says about the fasting person), 'He has left his food, drink and desires for My sake. The fast is for Me. So I will reward (the fasting person) for it and the reward of good deeds is multiplied ten times." Bukhari (there is also a hadeeth in Maliks Muwatta with a similar meaning)
Therefore the true believer who fasts according to what Allah SWT has commanded will be compelled to avoid evil speech and actions, therefore encouraging the believer to be consciously aware of what they are doing and saying at all times during the fast. A pattern of regular fasting makes the believer become accustomed to considering these matters on a daily basis leaving the beneficial effect of an improvement of their behaviour and worship towards Allah SWT at all times.
The last, and very significant benefit of fasting is that the prayers and dua of a fasting person are not rejected, as shown in the report that our Prophet (peace and blessings of Allah be upon him) said: "There are three prayers that are not rejected: the prayer of a father for his child, the prayer of the fasting person and the prayer of the traveller." Narrated by al-Bayhaqi in Saheeh al-Jami', Muslim and Bukhari
Prophet SAW observed voluntary fasts on Mondays and Thursday
Abu Hurairah reported that the most the Prophet would fast would be Monday and Thursday. He was asked about that and he said: "The actions are presented on every Monday and Thursday. Allah forgives every Muslim or every believer, except for those who are boycotting each other. He says [about them]: 'Leave them.' " This is related by Ahmad with a sahih chain.
And
Abu Qatada Ansari (Allah be pleased with him) reported that Allah's Massenger (may peace be upon him) was asked about fasting on Monday, whereupon he said: It is (the day) when I was born and revelation was sent down to me. Muslim
Ya Allah, grant us all the strength of Eeman and Taqwa to perform as many voluntary deeds as we can for Your sake, Ameen.