Does eating or drinking while fasting due to forgetfulness invalidate the fast?
General Chapter
Al-Mughni
Book of Fasting
Primary text
If one eats or drinks while fasting due to forgetfulness, the fast is not invalidated. This is the position held by Ali, Abu Hurayrah, Ibn Umar, 'Ata', Tawus, Ibn Abi Dhi'b, Al-Awza'i, Al-Thawri, Al-Shafi'i, Abu Hanifah, and Ishaq. The evidence is the saying of the Messenger of Allah, peace be upon him, as narrated by Abu Hurayrah: "If one of you eats or drinks forgetfully, let him complete his fast, for Allah has fed him and given him drink." (Agreed upon). In another narration, it is stated: "Whoever eats or drinks forgetfully, his fast is not broken, for Allah has provided for him as sustenance." Moreover, this is an act of worship that involves both prohibition and allowance, thus its prohibitions can be differentiated between intentional commission and omission, similar to prayer and Hajj.
Supporting text
Rabi'ah and Malik hold that the fast is invalidated because what is not valid when done intentionally with an act of the same type (like sexual intercourse) is also not permissible when done out of forgetfulness, similar to omitting the intention. However, the omission of the intention is not an act, and intention is a prerequisite (shart), and prerequisites are not waived by forgetfulness, unlike nullifiers. Also, the ruling for sexual intercourse is more severe, and it is possible to guard against it.