Question Summary:
Difference Between ‘forgetfully eating’ and ‘mistakenly eating’ while fasting

Question Detail:

Q: I forgetfully ate whilst fasting? A: If one was totally unaware that he was fasting, the fast will not be broken regardless of what was consumed.
 
Q: By mistake I swallowed water whilst doing wudhu? A: By doing an act mistakenly will break one's fast.  However, only Qadhā will be necessary.
 
How are these different if the person making wudhu forgets he’s fasting and swallows water to the person who forgets he’s fasting and eats?

Answer :

In the Name of Allah, the Most Gracious, the Most Merciful.
As-salāmu ‘alaykum wa-rahmatullāhi wa-barakātuh.
Your confusion stems from misunderstanding the wording used in the two rulings. The ruling does not change based on whether a person ate or drank. Rather, the difference in ruling is based on forgetfully or mistakenly eating, drinking or indulging in intimacy.
There is a difference between a person forgetfully consuming something and a person mistakenly consuming something. Forgetfully consuming something refers to a situation when a person has completely forgotten that he is fasting and he consumes something in this condition. Whilst mistakenly consuming something means, that a person is conscious of the fact that he is fasting, yet he unintentionally swallows something.[1]
Eating or drinking forgetfully will not nullify a person’s fast, whereas mistakenly doing so will nullify it.
 
And Allah Ta’āla Knows Best
Nabeel Valli
Student Darul Iftaa
Lusaka, Zambia
Checked and Approved by,
Mufti Ebrahim Desai.
www.daruliftaa.net