I woke up yesterday, needing to drink some water. I looked at the clock, and it was 3:30, so I said to myself: We do not know the exact time of the adhaan, so let me drink some water. Please note that I am in Vienna, and we cannot hear the adhaan; every mosque gives times different from the other mosques. My question is: do I have to make up this day, or is my fast valid?

Praise be to Allah

If the fasting
person is not sure whether dawn has broken, and he has no clear indication
that it has definitely broken, if he has sahoor at this time, there is no
blame on him and his fast is valid.

That is because
Allah, may He be exalted, says (interpretation of the meaning):


“And
eat and drink until the white thread of dawn becomes distinct to you from
the black thread [of night]. Then complete the fast until the sunset”


[al-Baqarah
2:187].

So stopping
eating and drinking is connected to certainty that dawn has broken, not to
merely thinking that that may or may not be the case.

Shaykh ‘Abd
ar-Rahmaan as-Sa‘di (may Allah have mercy on him) said:

“And
eat and drink until the white thread of dawn becomes distinct to you from
the black thread [of night].”
This refers to the time when one should stop eating, drinking and having
intercourse.

It indicates
that if a person is eating and so on, and is not sure whether dawn has come,
there is no blame on him.

End quote from
Tafseer as-Sa‘di (p. 87).

Ibn Qudaamah
(may Allah have mercy on him) said:

If someone who
is not sure whether dawn has broken eats, and the matter is not clear to
him, then he does not have to make up the fast, and he may continue to eat
until he becomes certain that dawn has broken. This was stated by Ahmad, and
is also the view of Ibn ‘Abbaas, ‘Ataa’, al-Awzaa‘i, ash-Shaafa‘i, and as-haab
ar-ra’y. Something similar was narrated from Abu Bakr as-Siddeeq and Ibn
‘Umar (may Allah be pleased with him).

That is
supported by the verse (interpretation of the meaning): “And
eat and drink until the white thread of dawn becomes distinct to you from
the black thread [of night]”,
so the time for eating extends until one becomes certain, and that may be
preceded by some uncertainty. If it were obligatory for him to make up that
day, then it would be forbidden for him to eat [at the time of uncertainty].

The Prophet
(blessings and peace of Allah be upon him) said: “So eat and drink, until
Ibn Umm Maktoom gives the adhaan.” He was a blind man, and he did not give
the adhaan until he was told that dawn had broken.

So the basic
principle is that it is still night, and the time of uncertainty is part of
the night, so long as it is not known for certain that night has ended.

End quote from
al-Mughni (4/390-391).

Shaykh al-Islam
Ibn Taymiyah (may Allah have mercy on him) said:

If he is not
certain as to whether dawn has broken or not, he may carry on eating and
drinking until he is certain that dawn has broken, and if he comes to know
after that that he ate after dawn had broken, there is a difference of
scholarly opinion as to whether he is obliged to make up that day.

The view that is
more likely to be correct is that he does not have to make it up. This is
narrated from ‘Umar, and was also the view of a number of the earlier and
later generations. And the view that he must make it up is the well-known
view among the fuqaha’ of the four madhhabs. And Allah knows best.

End quote from
Majmoo‘ al-Fataawa (25/216-217).

Conclusion:

With regard to
the time that you asked about, if in your city that is a time when there
could be uncertainty as to whether dawn has broken, then there is nothing
wrong with eating and drinking at that time, for the one who intends to
fast, and his fast is valid.

And Allah knows
best.