Intention for Fasting

I heard Allah's Messenger (ﷺ) saying, "The reward of deeds depends upon the intentions and every person will get the reward according to what he has intended. So whoever emigrated for worldly benefits or for a woman to marry, his emigration was for what he emigrated for."

Asma bint Abi Bakr said, "We broke our fast during the lifetime of the Prophet (ﷺ) on a cloudy day and then the sun appeared." Hisham was asked, "Were they ordered to fast in lieu of that day?" He replied, "It had to be made up for." Ma`mar said, "I heard Hisham saying, "I don't know whether they fasted in lieu of that day or not."

"The Messenger of Allah said on the day of Ashura: Is there anyone among you who has eaten today?' They said: Some of us are fasting and some of us are not.' He said: 'Do not eat for the rest of the day, and send word to the people of Al-Al-Arud telling them not to eat for the rest of the day."'

"The Messenger of Allah came to me one day and said: 'Do you have anything (to eat)?' I said: 'No.' he said: 'Then I am fasting.' Then he came to me after that day, and I had been given some Hais. I had kept some for him as he liked Hais. She said: 'O Messenger of Allah, we have been given some Hais and I kept some for you.' He said: 'Bring it here. I started the day fasting.' Then he ate some of it, then he said: 'The likeness of a voluntary fast is that of a man who allocated some of his wealth to give in charity; if he wishes he may go ahead and give it, and if he wishes he may keep it."'

"The Messenger of Allah passed by my door. He said: 'Do you have anything (to eat)?' I said 'I do not have anything.' He said 'Then he passed by my door a second time and we had been given some Hais. I brought it to him and he ate, and I was surprised. I said: 'O Messenger of Allah, you were fasting, then you ate Hais.' He said: 'Yes, O 'Aishah. The one who observes a fast other than in Ramadan, or making up a missed Ramadan, fast, is like a man who allocated some of is wealth to give in charity; if he wishes he may go ahead and give it, and if he wishes he may keep it."'

I asked 'Aishah: Would the Messenger of Allah (ﷺ) fast three days every month ? She replied: Yes. I asked: Which days in the month he used to fast ? She replied: He did not care which days of the month he fasted.

the Prophet said: "Whoever did not decide to fast before Fajr then there is no fast for him."

"Every good deed of the son of Adam will be multiplied manifold. A good deed will be multiplied ten times up to as many as seven hundred times, or as much as Allah wills. Allah says: "Except for fasting, which is for Me and I shall reward for it. He gives up his desire and his food for My sake.' The fasting person has two joys, one when he breaks his fast and another when he meets his Lord. The smell that comes from the mouth of a fasting person is better before Allah than the fragrance of musk."

Messenger of Allah (ﷺ) was even shier than a virgin behind her veil. When he saw something which he disliked, we could perceive it on his face.

[Al-Bukhari and Muslim].