`Aa’ishah said : The Messenger of Allah, salla Allahu alaihi wa salam, used to fast Mondays and Thursdays”. [an-Nasaa'i; Sahih]

Abu Hurairah reported that the most the Prophet, salla Allahu alaihi wa salam, would fast would be Monday and Thursday. He was asked about that and he said: “The deeds of people are presented to Allah on every Monday and Thursday. Allah forgives every Muslim except for those who are deserting each other. He says: “leave them for later.” [Ahmad; Hasan]

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Reward of Fasting in general (taken from Sahih Muslim):

Abu Sa’id al-Khudri (Allaah be pleased with him) reported Allaah’s Messenger (sallAllaahu alayhi wa sallam) as saying: He who observes fast for a day in the way of Allaah He would remove his face from the Hell to the extent of seventy years’ distance. No. 2572

Sahl b. Sa’d (Allaah be pleased with him) reported Allaah’s Messenger (sallAllaahu alayhi wa sallam) 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. No. 2569

Abu Huraira (Allaah be pleased with him) reported Allaah’s Messenger (sallAllaahu alayhi wa sallam) as saying: Every (good) deed of the son of Adam would be multiplied, a good deed receiving a tenfold to seven hundredfold reward. Allaah, 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 Allaah than the fragrance of musk. No. 2567

Abu Huraira reported Allaah’s Messenger (sallAllaahu alayhi wa sallam) as saying: Fasting is a shield. No. 2565

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….He who fasts all the year is as he who did not fast at all. The fasting of three days (a month) will be equal to the fasting of the whole year.”…. Bukhari Hadeeth No. 1862
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Narrated ‘Abdullah bin ‘Amr bin Al-’As: Allah’s Apostle said to me, “O ‘Abdullah! Have I not been informed that you fast during the day and offer prayers all the night.” ‘Abdullah replied, “Yes, O Allah’s Apostle!” The Prophet said, “Don’t do that; fast for few days and then give it up for few days, offer prayers and also sleep at night, as your body has a right on you, and your wife has a right on you, and your guest has a right on you. And it is sufficient for you to fast three days in a month, as the reward of a good deed is multiplied ten times, so it will be like fasting throughout the year.” I insisted (on fasting) and so I was given a hard instruction. I said, “O Allah’s Apostle! I have power.” The Prophet said, “Fast like the fasting of the Prophet David and do not fast more than that.” I said, “How was the fasting of the Prophet of Allah, David?” He said, “Half of the year,” (i.e. he used to fast on every alternate day).
Afterwards when ‘Abdullah became old, he used to say, “It would have been better for me if I had accepted the permission of the Prophet (which he gave me i.e. to fast only three days a month).”
Bukhari Hadeeth No. 1858

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http://www.sahihalbukhari.com/sps/sbk/
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