Note that the time for Fajr prayer begins when the second dawn starts, which is the white line that spreads horizontally along the horizon right and left. The time lasts until the sun rises.
The first dawn is the false dawn, which is whiteness that appears vertically in the sky like pillars. This happens approximately twenty minutes before the true dawn, and it increases and decreases according to the season.
It is known that the rulings apply to the true dawn, not the false dawn.
There are many ahaadeeth which speak about the two dawns, such as the following:
The Prophet SAWS (peace and blessings of Allaah be upon him) said: “There are two dawns, the dawn when food becomes haraam and prayer becomes permissible, and the dawn when prayer (i.e., Fajr prayer) is haraam and food is permitted.”
(Narrated by al-Haakim and al-Bayhaqi from the hadeeth of Ibn ‘Abbaas; classed as saheeh by al-Albaani in Saheeh al-Jaami’, 4279).
And the Prophet (peace and blessings of Allaah be upon him) said: “There are two dawns. With regard to the dawn which is like the tail of a wolf, this does not make it permissible to pray and haraam to eat. With regard to the dawn which appears horizontally in the sky, this makes it permissible to pray and forbidden to eat.”
(Narrated by al-Haakim and al-Bayhaqi from the hadeeth of Jaabir; classed as saheeh by al-Albaani in Saheeh al-Jaami’, 4278)
According to another report, “There are two dawns. One is called the tail of the wolf, which is the false dawn that appears vertically, not horizontally. The other appears horizontally and not vertically.” (Classed as saheeh by al-Albaani in al-Silsilah al-Saheehah, no. 2202).
And the Prophet (peace and blessings of Allaah be upon him) said, “Do not let the adhaan of Bilaal stop you from eating suhoor, or the vertical dawn, but the dawn which appears along the horizon.”
(Narrated by Abu Dawood and al-Tirmidhi, who classed it as hasan. Classed as saheeh by al-Albaani in Saheeh al-Tirmidhi, no. 568)
From this explanation given by the Prophet (peace and blessings of Allaah be upon him), we know that the definition of the time of Fajr is based on observation, not on astronomical calculations or on timetables whose authors are unknown as far as their trustworthiness and knowledge are concerned, especially if it is proven that they do not give the correct times.
This mistake does not occur only in Egypt, rather it seems that most of the timetables do not give the correct time for Fajr and are based on the false dawn. This means that there is the risk that the Muslims’ prayers are invalid, especially in the case of those who pray in their houses immediately after hearing the adhaan.
A group of scholars and researchers in the Kingdom of Saudi Arabia, Syria, Egypt and Sudan have attempted to find out the time of the true dawn, and it is clear to them that the timetables in use at present are incorrect.
Shaykh al-Albaani (may Allaah have mercy on him) said:
“I have seen that myself many times in my house, in the Hamlaan mountains to the south-east of Amman, and that enables me to confirm what some of those who are keen that the Muslims’ worship should be correct have said, that the adhaan of Fajr in some Arab countries is given 20-30 minutes before the time of the true dawn, i.e., it is also before the time of the false dawn. I have often heard the iqaamah for Fajr being given in some mosques at the time when the true dawn begins, and they give the adhaan before it is time. And they may hasten to do the fard prayer before it is time during the month of Ramadaan.”
(from al-Silsilah al-Saheehah, 5/25)
Once this is understood, the people from each town or city should appoint a group of trustworthy scholars to find out the time of Fajr and to announce that to the people, and warn them against following timetables if it is proven that they are incorrect.
The brother who asked this question, and all Muslims, should not pray Fajr until they are certain or think it most likely that dawn has broken; if they can delay the adhaan until this time, they should do that. They should also explain this ruling to their wives and daughters, lest they end up doing the prayer at the wrong time.
And Allaah knows best.