When should a person break his/her fast

Narrated 'Abdullah bin Abi Aufa" :-
    
    We were traveling with Allah's Apostle ( Peace be upon Him.) and he was fasting, and when the sun set, he said to someone:-
     "Get down and mix Sawiq with water for us." He replied, "O Allah's Apostle! Will you wait till it is evening?"
    
    The Prophet ( Peace be upon Him.) again said:-
    "Get down and mix Sawiq with water for us."
    
    He replied, "O Allah's Apostle! It is still daytime." The Prophet( Peace be upon Him.)  said again,:-
    
    "Get down and mix Sawiq with water for us."
     So, he got down and carried out that order.
    
    The Prophet( Peace be upon Him.)  then said:-
    
     "When you see night falling from this side, the fasting person should break his fast," and he beckoned with his finger towards the east.

S. Bukhari -Volume 3, Book 31, Number 177:


Narrated Sahl bin Sad:-

    Allah's Apostle( Peace be upon Him.)  said:-
    
     "The people will remain on the right path as long as they hasten the breaking of the fast."
    
S. Bukhari-Volume 3, Book 31, Number 178.