The true time of Fajr

Firstly: 

We ask Allah to reward you with the best of rewards for your
eagerness to learn the truth and do the right thing in your worship. We ask
Allah, may He be exalted, to guide you and increase you by His grace in your
love for knowledge and your keenness to learn. It should be noted that there
are two dawns, the false dawn (al-fajr al-kaadhib), which does not signal
the beginning of the time for Fajr prayer or the time when the one who wants
to fast should refrain from food, drink and intercourse; and the true dawn
(al-fajr al-saadiq), which is when the time for Fajr prayer begins and the
time when the one who wants to fast should refrain from food, drink and
intercourse. This is what is referred to in the verse in which Allah, may He
be exalted, says (interpretation of the meaning): “and
eat and drink until the white thread (light) of dawn appears to you distinct
from the black thread (darkness of night)” [al-Baqarah 2:187]. 

The Prophet (blessings and peace of Allah be upon him)
explained the difference between them in many hadeeths, some of which speak
of the difference between them in terms of characteristics, and others speak
of the difference between them in terms of rulings; and some hadeeths
mention both characteristics and rulings. 

You can see these hadeeths in the answer to question no.
26763 

The difference between the two dawns also appears clearly in
the words of the Sahaabah and Taabi‘een and the imams who came after them. 

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

‘Abd al-Razzaaq said: Ibn Jurayj told us that ‘Ata’ said: I
heard Ibn ‘Abbaas say: There are two dawns: as for that which appears
vertically in the sky, it does not make anything halaal or haraam; rather
the dawn that appears along the mountaintops is that which makes it haraam
to drink. 

‘Ata’ said: If it appears vertically in the sky, that does
not make it haraam to drink for fasting or praying, and it does not affect
Hajj. But if it spreads along the mountaintops, it becomes haraam to drink
for one who is fasting, and it means that Hajj has been missed. 

This is a saheeh isnaad going back to Ibn ‘Abbaas and ‘Ata’.
Something similar was also narrated from more than one of the salaf (may
Allah have mercy on them). 

Tafseer Ibn Katheer, 1/516 

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

To sum up, the time of dawn refers to the appearance of the
second dawn according to consensus. That is indicated by the reports of the
times of prayer. It is the white line that appears along the horizon; it is
called the true dawn (al-fajr al-saadiq). 

As for the first dawn, it is the white line that appears
vertically and not horizontally. It is not connected to any ruling and it is
called the false dawn (al-fajr al-kaadhib).  

Al-Mughni, 1/232 

Shaykh Ibn ‘Uthaymeen (may Allah have mercy on him) said: 

The scholars stated that there are three differences between
it (the false dawn) and the second (dawn): 

1.    
The first dawn is vertical and
not horizontal, i.e., it extends from east to west (across the arc of the
sky) whereas the second dawn extends from north to south (across the
horizon).

2.    
The first dawn turns dark,
i.e., this light appears for a short while, then it goes dark, whereas the
second dawn does not turn dark, rather it increases in light and grows
brighter.

3.    
The second dawn extends along
the horizon with no darkness between it and the horizon, whereas the first
dawn is separate from the horizon and there is darkness between it and the
horizon. 

Are any rulings connected to the first dawn? No shar‘i
rulings whatsoever are connected to it, such as stopping eating when you
want to fast, or the time for Fajr prayer beginning. The rulings are
connected to the second dawn. End quote. 

Al-Sharh al-Mumti‘, 2/107, 108 

Secondly: 

With regard to the available prayer timetables, they are not
a reliable source for finding out the time of Fajr prayer. The fact that
these timetables are incorrect has been proven. 

What you should do is not rely on the timetables to find out
the time of Fajr prayer. You have to look for the correct time on the basis
of what we have mentioned of the differences between the false dawn and the
true dawn. If you cannot look at the sky every day, then you can delay it
after the time mentioned in the timetable, to be on the safe side. In our
country this time differs from one city to another and from one season to
another. So you can delay it half an hour, for example, to pray Fajr, but to
be on the safe side you should stop eating and drinking before that. 

You can draw up a correct timetable to be used by those who
come after you, after working out the time of the true dawn for a whole
year, at various times. Perhaps you will attain the reward of correcting the
Muslims’ acts of worship. 

Based on that, if possible you can work out the time of Fajr
yourselves and follow that in prayer and fasting. If that is not possible,
then you should not pray until you think it most likely that the time for
the prayer has begun. 

With regard to fasting, you can eat or drink until you are
certain that dawn has broken, because Allah, may He be exalted, says
(interpretation of the meaning): “and eat and
drink until the white thread (light) of dawn appears to you distinct from
the black thread (darkness of night)” [al-Baqarah 2:187].

Shaykh Ibn ‘Uthaymeen (may Allah have mercy on him) said: 

So long as he is not certain that dawn has broken, he may eat
even if he is not sure, until he is certain. End quote. 

Fataawa al-Siyaam, p. 299 

And Allah knows best.