Praise be to Allaah.  

Al-Bukhaari (1921) narrated from Anas that Zayd ibn Thaabit said: “We ate suhoor with the Prophet (peace and blessings of Allaah be upon him), then he stood up to pray.” I [Anas] said: “How long was there between the adhaan and suhoor?” He said: “As long as it takes to recite fifty verses.”

 This hadeeth indicates that the Prophet (peace and blessings of Allaah be upon him) used to eat suhoor this amount of time before the adhaan, not that the Prophet (peace and blessings of Allaah be upon him) started to fast and stopped eating and drinking this amount of time before Fajr. There is a difference between the time of suhoor and the time of stopping eating and drinking. This is clear, praise be to Allaah. It is like saying, “I ate suhoor two hours before Fajr.” This does not mean that you started fasting from that time, rather you are simply stating what time you ate suhoor. 

What may be understood from the hadeeth of Zayd ibn Thaabit (may Allaah be pleased with him) is that it is mustahabb to delay suhoor and it is not mustahabb to stop eating and drinking a while before Fajr. 

Allaah has permitted those who intend to fast to eat and drink until they are certain that dawn has come. Allaah 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), then complete your Sawm (fast) till the nightfall”

[al-Baqarah 2:187] 

So it is permissible to have intercourse, eat and drink during the nights of Ramadaan from the beginning of the night until dawn comes, then we are commanded to complete the fast until night comes.  

Stated by Abu Bakr al-Jassaas in Ahkaam al-Qur’aan, 1/265. 

Al-Bukhaari (1919) and Muslim (1092) narrated from ‘Aa’ishah (may Allaah be pleased with her) that Bilaal used to give the adhaan at night, and the Messenger of Allaah (peace and blessings of Allaah be upon him) said: ‘Eat and drink until Ibn Umm Maktoom gives the adhaan, for he does not give the adhaan until the dawn comes.” 

Al-Nawawi said in al-Majmoo’ (6/406): 

Our companions and other scholars are agreed that suhoor is Sunnah, and that delaying it is preferable. The evidence for all of that is the saheeh ahaadeeth. And because suhoor and delaying suhoor helps one to fast, and they involve being different to the kuffaar. Moreover the time for fasting is the day, so there is no sense in delaying iftaar or refraining from eating suhoor at the end of the night. 

The Standing Committee (10/284) was asked: I read in some tafseers that the fasting person should stop eating and drinking 20 minutes before the adhaan of Fajr, and this is described as being on the safe side. How much time should there be between stopping eating and drinking and the adhaan of Fajr in Ramadaan? What is the ruling on one who hears the muezzin saying “al-salaatu khayrun min al-nawm (prayer is better than sleep)” and he says can still drink so long as the adhaan is still going on. Is this correct? 

They replied: 

The basic principle regarding when the fasting person should stop eating and drinking and should break the fast is the verse in which Allaah 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), then complete your Sawm (fast) till the nightfall”

[al-Baqarah 2:187] 

It is permissible to eat and drink until the dawn appears, which is the white thread of light that Allaah has made the latest time when it is permissible to eat and drink. When the second dawn appears, it is haraam to eat and drink and do other things that break the fast. Whoever drinks whilst hearing the adhaan for Fajr, if the adhaan comes after the second dawn, then he has to make up that day, but if that was before dawn, then he does not have to make it up. 

Shaykh Ibn Baaz was asked about making the time for stopping eating and drinking approximately fifteen minutes before Fajr. He replied: 

I do not know of any basis for this, rather what is indicated by the Qur’aan and Sunnah is that we should stop eating and drinking when dawn comes, because Allaah 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), then complete your Sawm (fast) till the nightfall”

[al-Baqarah 2:187] 

And the Prophet (peace and blessings of Allaah be upon him) said: “Dawn is of two types, a dawn when it becomes haraam to eat and permissible to pray, and a dawn when you should not pray [i.e., Fajr prayer] and it is permissible to eat.” Narrated by Ibn Khuzaymah and al-Haakim, who classed it as saheeh in Buloogh al-Maraam. And the Prophet (peace and blessings of Allaah be upon him) said: “Bilaal gives the adhaan at night, so eat and drink until Ibn Umm Maktoom gives the call to prayer.” The narrator said: Ibn Umm Maktoom was a blind man who did not give the call to prayer until someone said to him, ‘Morning has come, morning has come.’” Saheeh – agreed upon. 

Majmoo’ Fataawa Ibn Baaz, 15/281.