Abu Hurayrah (may Allah be pleased with him) reported that the Messenger of Allah (may Allah's peace and blessings be upon him) said: "Allah, Glorified and Exalted, said: 'All the actions of of the son of Adam are for him, except for fasting. Indeed, it is for Me, and I give reward for it.' Fasting is a shield. So when one of you is fasting, then let him not say obscene speech or make too much noise, and if someone insults him or fights him, then let him say: 'I am fasting.' (I swear) by the One in Whose hand the soul of Muhammad is! The foul smell that emanates from the mouth of the fasting person is more pleasant in the sight of Allah than the smell of musk. The fasting person has two (moments of) joy: one when he breaks his fast, as he feels happy, and the other when he meets his lord, he is happy with his fast."
This is the wording of Al-Bukhāri's narration.
In another version by Al-Bukhāri: "He leaves his food, drink, and sexual desire for My sake. Fasting is for me, and I will reward it, and a single good deed is worth ten."
According to the narration of Muslim: "Every action of the son of Adam is multiplied, and a single good deed is worth ten till seven hundred times. Allah, the Exalted, says: '(This is so) except for fasting, for indeed it is for Me, and I will reward it. He leaves his desires and food for My sake.' For the fasting person, there are two moments of joy; a moment of joy when he breaks his fast, and a moment of joy when he meets his lord. Verily, the unpleasant smell coming from the mouth of the fasting person is more fragrant with Allah than the smell of musk."
Sahl ibn Sa‘d (may Allah be pleased with him) reported: The Prophet (may Allah's peace and blessings be upon him) said: "There is a gate in Paradise called Ar-Rayyān through which only those who fast will enter on the Day of Resurrection. No one else will enter through it. It will be called out: ‘Where are those who used to fast?’ So they will stand up and proceed towards it. When the last of them has entered, the gate will be closed, and no one else will enter through it.'"
Abu Hurayrah (may Allah be pleased with him) reported that the Prophet (may Allah's peace and blessings be upon him) said: "He who observes fasting during the month of Ramadan faithfully and expecting its reward from Allah will have his past sins forgiven."
‘Abdullāh ibn ‘Abbās (may Allah be pleased with him) reported: The Messenger of Allah (may Allah’s peace and blessings be upon him) was the most generous of people, and he used to be more generous than ever in Ramadan, when Jibrīl would meet him. He used to meet him every night during Ramadan to revise the Qur'an with him. Indeed, the Messenger of Allah (may Allah’s peace and blessings be upon him) was more generous than the fast wind.
‘Abdullāh ibn ‘Umar (may Allah be pleased with him) reported: I heard the Messenger of Allah (may Allah's peace and blessings be upon him) saying: "Observe the fast when you see it (the new moon of Ramadan), and break the fast when you see it (the new moon of Shawwāl), but if the sky is overcast and you cannot see it, then act on estimation (by counting Sha‘bān as 30 days)."