It was narrated on the authority of Hafsah bint ‘Umar, may Allah be pleased with her, that the Messenger of Allah, said: “Whoever does not resolve on fasting before dawn, his fasting is invalid.” [Abu Daawood and At-Tirmithi] The sound judgment concerning this Hadeeth (narration) is that it is Mawqoof (a Hadeeth narrated by a Companion in which the chain of narration does not reach the Messenger of Allah, ).
Another version reads: “Whoever does not have the intention of fasting before dawn, his fasting is invalid.” [An-Nasaa’i]
‘Abdullaah ibn ‘Umar, may Allah be pleased with him, was reported to have said, “Only those who resolve on fasting before dawn, their fasting is valid.” [Maalik]
The first Hadeeth indicates that the Muslim who does not intend and resolve before dawn to fast, his fasting is invalid.
At-Tirmithi said, “Scholars believe that this Hadeeth means that the Muslim who does not have an intention for fasting before dawn during the month of Ramadan, or outside the month of Ramadan when making up for missed days or for vowed fasting, if such a person does not have the intention at night that he will fast the next day, then his fasting will not avail him. In case of voluntary fasting, however, it is permissible for him to intend the fasting even in the morning as said by Ash-Shaafi‘i, Ahmad and Is-haaq.”
Benefits and rulings:
First: For fasting, one must have the intention of worshipping Allah The Almighty. Hence, if one abstains from the annulments of fasting for the sake of a diet or medical reasons or because he does not have a desire for food or the like, then his fasting is invalid under Sharee‘ah (Islamic legislation) and he will not be rewarded for it.
Second: The intention lies in the heart, so if it crosses the mind of someone that he will fast the next day, then he has developed the intention for fasting.
Third: The obligatory fasting of Ramadan, or for an oath, or for expiation, must start from dawn until sunset, and this cannot be achieved except by a person who intends fasting before dawn. However, a person makes the intention for that during daytime, his fasting misses a part of the day, and thus his fasting is invalid. That is why the intention for obligatory fasting must be made before dawn.
Fourth: It is permissible to have the intention for the obligatory or voluntary fasting at any time of the previous night. The intention is not rescinded if it is followed by something that annuls the fast and it does not need to be renewed.