Fasting lasts until the sun sets and is not as some of the Shi’ah say
Question

                I am asking about the topic of fasting and breaking the fast. I was speaking to my neighbours who follow the Shi’i madhhab, and they recited to me a verse of Qur'aan which says that fasting is from the time of the white thread until night, and it is not until sunset only. This is what they said to me. I hope that you can advise me, may Allah reward you with the best of rewards.
Praise be to Allah.
    The time of fasting on which the Muslims are unanimously 
    agreed and which they have followed from the time of the Prophet (blessings 
    and peace of Allah be upon him) and his Companions until the present day is 
    from the break of the true dawn until when the disk of the sun disappears 
    completely beneath the horizon. This is indicated by the Qur'aan and Sunnah 
    and definitive consensus of the Muslims. 

    Allah says (interpretation of the meaning): “then complete 
    your Sawm (fast) till the nightfall [al-layl]” [al-Baqarah 2:187]. 
    Al-layl [translated here as nightfall] in the language of the Arabs 
    starts when the sun sets. 

    It says in al-Qamoos al-Muheet (1364): al-Layl: 
    from the setting of the sun until the break of the true dawn or sunrise. End 
    quote. 

    It says in Lisaan al-‘Arab (11/607): al-Layl: 
    comes straight after the end of al-Nahaar (day), and starts when the 
    sun sets. End quote. 

    Al-Haafiz Ibn Katheer (may Allah have mercy on him) said in 
    his commentary on this verse:

    The words of Allah “then complete your Sawm (fast) till 
    the nightfall” imply that breaking the fast at the moment of sunset is a 
    shar’i rule. End quote. 

    Tafseer al-Qur’aan al-‘Azeem, 
    1/517 

    In fact some commentators have pointed out that the use of 
    the preposition ila (till) in this verse also implies hastening, 
    because that preposition indicates reaching the end and achieving the goal. 

    Al-‘Allaamah al-Taahir ibn ‘Ashoor (may Allah have mercy on 
    him) said:

    Ila al-layl (till the nightfall) means until one achieves 
    that goal and reaches the night, and the preposition ila is chosen to 
    indicate that one should hasten to break the fast when the sun sets, because 
    the preposition ila means that the purpose is achieved then, unlike the 
    preposition hatta (until). What is meant here is to indicate that the fast 
    is completed when the night begins. End quote. 

    Al-Tahreer wa’l-Tanweer, 1/181 

    All of that is supported by what is narrated in 
    al-Saheehayn from Ameer al-Mu'mineen ‘Umar ibn al-Khattaab (may Allah be 
    pleased with him) who said: The Messenger of Allah (blessings and peace of 
    Allah be upon him) said: “When the night comes from here and the day departs 
    from here, and the sun sets, then it is time for the fasting person to break 
    his fast.” Narrated by al-Bukhaari (1954) and Muslim (1100). 

    In this hadeeth the coming of night from the east and the 
    disappearance of the disk of the sun below the horizon are mentioned 
    together, which is something that is well known, because darkness starts 
    from the East as soon as the light of the sun disappears below the horizon. 
    Al-Haafiz Ibn Hajar (may Allah have mercy on him) said:

    The phrase “when night comes from here” means from the east, 
    and what is meant is when darkness becomes discernible. In this hadeeth he 
    mentioned three things, because even though they are interconnected in fact, 
    they may appear not to be connected, and it may be thought that night is 
    coming from the east when it has not yet come, because something is covering 
    the light of the sun; the same is also true of the departure of day. Hence 
    it is clarified by the words “and the sun sets”, as an indication that it is 
    essential to confirm that night has come and day has gone, and that these 
    events occur because of the setting of the sun and not for any other reason. 
    End quote. 

    Fath al-Baari, 4/196 

    Al-Nawawi (may Allah have mercy on him) said: 

    The scholars said: each of these three things implies the 
    other two and is interconnected with them. Rather he mentioned them together 
    because a person may be in a valley and the like in such a way that he 
    cannot see the setting of the sun, so he relies on the coming of darkness 
    and the disappearing of daylight. End quote. 

    Sharh Muslim, 7/209 

    Al-Bukhaari (1955) and Muslim (1101) narrated that 
    ‘Abd-Allaah ibn Abi Awfa (may Allah be pleased with him) said: We were with 
    the Messenger of Allah (blessings and peace of Allah be upon him) on a 
    journey and he was fasting. When the sun set, he said to one of the people: 
    O So and so, get up and make saweeq for us (mix it with water so that we can 
    drink it). He said O Messenger of Allah, why not wait till the evening? He 
    said: Dismount and make saweeq for us. He said: O Messenger of Allah, why 
    not wait till the evening? He said: Dismount and make saweeq for us. He 
    said: It is still day. He said: Dismount and make saweeq for us. So he 
    dismounted and made saweeq for them, and the Prophet (blessings and peace of 
    Allah be upon him) drank it, then he said: When you see that night has come 
    from here, then let the fasting person break his fast. 

    Al-Haafiz Ibn Hajar (may Allah have mercy on him) said: 

    This hadeeth indicates that it is mustahabb to hasten to 
    break the fast and that it is not permissible to refrain from eating and 
    drinking for any part of the night at all; rather as soon as it is 
    established that the sun has set, it is permissible to break the fast. End 
    quote. 

    Fath al-Baari, 4/197. 

    Moreover, the fact that there is consensus among the Muslims 
    regarding breaking the fast and eating as soon as one hears the muezzin give 
    the call to Maghrib prayer when the sun disappears is evidence that this is 
    the truth and the one who goes against that is following something other 
    than the way of the believers and has introduced something into the religion 
    for which he has no proof or reports from the scholars. 

    Al-Nawawi (may Allah have mercy on him) said:

    Maghrib comes immediately after the sun has set, and this is 
    something on which there is consensus. Something concerning this was 
    narrated from the Shi’ah to which no attention should be paid and which has 
    no basis. End quote. 

    Sharh Muslim, 5/136 

    In fact, in many of the books of the Shi’ah it mentions that 
    on which there is consensus among the Muslims concerning this matter. Some 
    of them narrated from Ja’far al-Saadiq (may Allah have mercy on him) that he 
    said: “When the sun sets, it becomes permissible to break the fast and it 
    becomes obligatory to offer the prayer.” End quote. 

    Al-Baroojardi narrated from the author of al-Da’aa’im 
    that he said: We narrated from Ahl al-Bayt -- may the blessings of Allah be 
    upon them all -- that there was consensus concerning that which we learned 
    from the reports from them, that the onset of night which makes it 
    permissible for the fasting person to break the fast is the disappearance of 
    the sun beneath the western horizon without any barrier which would prevent 
    seeing it such as a mountain or wall and the like. When the disk disappears 
    beneath the horizon, then the night has begun and it is permissible to break 
    the fast. End quote. 

    Jaami’ Ahaadeeth al-Shi’ah, 
    9/165 

    To sum up: what are some of the Shi’ah do now, of delaying 
    Maghrib prayer and the breaking of the fast until sometime after the sun has 
    set is contrary to what is indicated by the Holy Qur'aan, the saheeh Sunnah 
    of the Prophet and the consensus of the Muslims. 

    Moreover it is contrary to what they themselves narrated from their Imams! 

    And Allah knows best.