The hadith was narrated by at-Tirmidhi (705) and Abu Dawud (2348) from Talq ibn `Ali, that the Messenger of Allah (blessings and peace of Allah be upon him) said: “Eat and drink, and do not let the vertical light stop you; eat and drink until the reddish light appears to you along the horizon.” It was classed as authentic (sahih) by al-Albani.
Ahmad (16291) also narrated from Talq that the Prophet (blessings and peace of Allah be upon him) said: “Dawn is not the vertical light that appears at the horizon; rather it is the horizontal reddish light.” This report was classed as sound (hasan) by the commentators on Al-Musnad.
What the hadith means is that there is a difference between the false dawn and the true dawn, and that the false dawn does not mean that one should stop eating and drinking.
The false dawn is the vertical light, and the true dawn is the horizontal, reddish light.
Al-Khattabi said in Ma`alim as-Sunan (2/105): The words “do not let the vertical light stop you” mean: … The vertical light is the light that goes upwards, before it appears along the horizon.
What is meant by the reddish light is that the white colour of the light is mixed with some reddish colour. When the white light is completely manifested, the reddish-coloured light starts to appear. The Arabs likened the dawn to a piebald horse, because of what it contained of white and red light. End quote.
It says in `Awn al-Ma`bud (6/339), after quoting the words of al-Khattabi: I say: The word ahmar (translated here as red or reddish) may also refer to abyad (white). It says in Taj al-`Arus: Ahmar may refer to that which is red in colour, and it may also refer to that which is white. Some interpreted the hadith “I have been sent to the red and the black” on that basis. And we may use the phrase imra’ah hamra’ (lit. red woman) to refer to one who is white. End quote.
What is meant by the Prophet’s words “until the reddish light appears to you along the horizon” is the white light, which appears when the light of day becomes distinct from the darkness of night. In other words, it refers to the true dawn. End quote.
There are two dawns: the false dawn, which is the vertical line that starts from the lowest horizon and rises up, like a pillar. This appears approximately twenty minutes before the true dawn, and maybe more or less, depending on the season.
The true dawn is the horizontal white light that extends right and left along the horizon.
Shaykh Ibn `Uthaymin (may Allah have mercy on him) said:
There are three differences between them:
After the false dawn, it gets dark again, and after the true dawn it only gets lighter.
The false dawn is vertical and the true dawn is horizontal.
There is darkness between the false dawn and the horizon; it is like a white pillar, but its lower part is dark. There is no darkness between the true dawn and the horizon.
These three differences are a natural occurrence and can be observed, but because of streetlights we cannot see that; but if you are in the wilderness with no lights around you, you will see the difference.
End quote from Fatawa Ibn `Uthaymin (7/337).
What is meant by the words of at-Tirmidhi (may Allah have mercy on him), “And this is the view of the scholars, that it is not prohibited, for the one who wants to fast, to eat and drink until the horizontal red dawn appears. This is the view of the majority of scholars” is:
Thus eating and drinking become prohibited when the true dawn appears, which is the horizontal or red dawn, meaning the reddish white light that begins to appear. It is not the redness that appears before sunrise.
See also the answer to question no. 93160.
And Allah knows best.
