Answered by Shaykh Amjad Rasheed
If at the end of the night, I have doubts about the time that dawn enters (because I am on the road), is it permissible for me to keep eating? Similarly, if at the end of the day, I have doubts about the time that the sun sets, can I start eating?
If a person who wants to fast has doubts about the time that dawn enters, it is permissible for him to keep eating. This is because the default is that it is still night.
It says in the Minhaj with the Tuhfa (3:411). “It is permissible to eat if one thinks that it is still night, whether by way of ijtihad or by being informed. And I [Nawawi] say: it is the same if one has doubts, meaning that one is uncertain because the default is that it is still night.”
So if one eats and then he finds out afterwards that dawn had entered, it is obligatory for him to stop eating and also to make up that fast, because finding out that one ate after dawn invalidates one’s fast. However, if he ate and didn’t find out that dawn had entered, then his fast is valid and he doesn’t have to make it up.
As for when a person is doubtful at the end of the day, whether the sun has set or not, it is not permissible for him to start eating unless he is certain that the sun is set. This is because the default is that it is still daytime, which is the opposite of the preceding issue. So if he purposely eats, while still in doubt, then he has sinned and his fast is invalidated.
Amjad Rasheed
[Translated by Sr. Shazia Ahmad]