If a person consumes something that breaks the fast due to ignorance of the ruling or of the time

So long as you did not know
that swallowing this food breaks the fast, then you do not have to make up
those days, because ignorance of things that break the fast is a valid
excuse, according to the correct view. 

Shaykh Ibn ‘Uthaymeen (may
Allaah have mercy on him) said: Things that break the fast and that may be
done voluntarily, do not break a person’s fast unless three conditions are
met: 

The first condition is that
he is aware, and the opposite of awareness is ignorance. 

So if a person eats
something and he is ignorant, then he does not have to make up that day.
Ignorance is of two types:  

(i)               
Ignorance of the ruling, such
as if a person vomits deliberately but he is not aware that vomiting breaks
the fast. In this case he does not have to make up the fast because he is
ignorant. The evidence that the one who is ignorant of the ruling does not
break his fast is the report that is proven in al-Saheehayn from the
hadeeth of ‘Adiyy ibn Haatim (may Allaah be pleased with him), who said that
he put two ropes – one black and one white – beneath his pillow. These were
ropes of the type used to hobble camels. He started looking at them, and
when he could distinguish between the white rope and the black one, he
stopped eating and drinking. The next day he went to the Prophet (peace
and blessings of Allaah be upon him) and told him about that. The Prophet
(peace and blessings of Allaah be upon him) said to him: “Your pillow
must be very wide, if the white thread and the black thread are beneath your
pillow. Rather that is the blackness of the night and the whiteness of the
day” But the Prophet (peace and blessings of Allaah be upon him) did
not tell him to make that day up, because he had been unaware of the meaning
of the verse. 

(ii)             
Ignorance of the time. For
example, if a person thinks that dawn has not yet broken, then he finds out
that it had broken. He does not have to make up that day. Similarly if a
person breaks the fast at the end of the day thinking that the sun has set,
then he finds out that it had not set, he does not have to make up that day
either. The evidence for that is the report narrated by al-Bukhaari from
Asma’ bint Abi Bakr (may Allaah be pleased with her) who said: We broke our
fast on a cloudy day at the time of the Prophet (peace and blessings of
Allaah be upon him), then the sun came out. The point here is that if the
fast was invalidated, it would have been obligatory to make it up, and if it
had been obligatory to make it up, the Prophet (peace and blessings of
Allaah be upon him) would have commanded them to do that. If he had ordered
them to make it up, this would have reached us because it is part of
preserving sharee’ah. As there is no report that says that the Messenger
(peace and blessings of Allaah be upon him) told them to do that, and
as he did not tell them to do that, it is known that the fast was not
invalidated, so it does not have to be made up in this case. But as soon as
a person realizes what the situation is, he must stop eating and drinking,
so that even if there is a morsel in his mouth, he has to spit it out. End
quote from Majmoo’ Fataawa al-Shaykh Ibn ‘Uthaymeen (19/116). 

Then he mentioned the
second and third conditions, which are that he should be aware of the
situation and observing the fast willingly. 

Thus it is known that you
do not have to make up these fasts.  

And Allaah knows best.