On the authority of Abu Hurayrah  (may Allāh be pleased with him) that the Prophet (صلى الله عليه وسلم)  said:

مَنْ نَسِيَ وَهُوَ صَائِمٌ، فَأَكَلَ أَوْ شَرِبَ، فَلْيُتِمَّ صَوْمَهُ، فَإِنَّمَا أَطْعَمَهُ اَللَّهُ وَسَقَاهُ – مُتَّفَقٌ عَلَيْهِ

Whoever forgets while he is fasting and he eats or drinks, let him continue (complete) his fast. Indeed it was only Allāh who fed him and gave him drink. (Agreed Upon)

The Noble Scholar Shaykh Ibn Bāz (may Allāh have mercy upon him) commented:

This is a virtue from Allāh (‘azza wa-jall). Mankind is prone to forgetfulness just as the Prophet  (صلى الله عليه وسلم) said: “I am a human being like you. I forget just as you forget.”
Forgetfulness is from human nature. Therefore if he forgets while he is fasting in Ramadan or fasting as an expiation or fasting for a reason other than these two and he eats or drinks or he has done another one of the things that breaks the fast out of forgetfulness, his fast is sound. This is based upon this authentic narration. In another wording collected by al-Ḥākim, “Whoever breaks his fast in Ramaḍān out of forgetfulness, it’s not upon him to make up the fast nor make an expiation for it.” If the person was to have relations or eat or drink out of forgetfulness, his fast is sound and there’s no expiation upon, no freeing of a slave, nor is it upon him to make up the fast if it was in a state of forgetfulness, and Allāh knows best the reality  (of affairs). Allāh knows the reality and Allāh will deal with him according to that which he is upon of truthfulness or lies.

However, if the person is truthful concerning his forgetfulness, it’s not upon him to make up the fast and his fast is sound. As for case if he was lying, this person’s affair is (left) to Allāh. The religious verdict will not benefit him even if a man was to give him a religious verdict (which is in his favor). If he is one who is lying (regarding him breaking his fast out of forgetfulness), upon him is a sin for that which he has done. However, as long as he is truthful regarding him being in a state of forgetfulness, indeed his fast is sound. Mankind is tested with forgetfulness and (at the same time) he is excused. Even in the prayer which is the greatest of the obligations, it’s possible that he can forget and it’s possible that he makes the salām (to end the prayer) and there’s a deficiency (in the prayer). It’s possible that he can leave off some of the pillars (of the prayer). If he does that, he implements that which Allāh has legislated in the prayer (when one forgets). If he forgets a unit, he comes with another unit and completes his prayer with the prostration of forgetfulness. If he forgets a pillar, he fulfills it. If he forgets an obligation, it’s obligation is removed from him, (he doesn’t have to make it up) and he prostrates for the forgetfulness.

Likewise in the case fasting. The matter is not by the choice of the person, for he has been created upon this characteristic; therefore, he forgets. The Prophet (صلى الله عليه وسلم) has even forgotten and he is the best of the creation. He forgot (something) while in the prayer. This is how the children of Adam are. They are tested with forgetfulness in the prayer and in other than it. Indeed the Messenger (صلى الله عليه وسلم) has clarified the rules of forgetfulness in the prayer and likewise in the fast. He informed  (us) that eating and drinking out of forgetfulness doesn’t harm him (in relation to his fast). Likewise him having relations and him receiving cupping (out of forgetfulness), it doesn’t harm him (in relation to his fast). All of that which has passed from the things that break the fast –  if he does it out of forgetfulness and he didn’t become aware until afterwards – his fast is sound.

Source: Ifhām fī Sharḥ `Umdatil-Aḥkām, pg.392 

Translated by Abu Yusuf Khaleefah
16th of Ramadaan, 1437 (06-21-2016)
Masjid Nur Allah, Queens, NYC

Original Arabic

قال الشيخ عبدالعزيز بن عبدالله بن باز رحمه الله تعالى

عن أبي هريرة – رضي الله عنه أن النبي صلى الله عليه وسلم -: «مَنْ نَسِيَ وَهُوَ صَائِمٌ فَأَكَلَ أَوْ شَرِبَ، فَلْيُتِمَّ صَوْمَهُ، فَإِنَّمَا أَطْعَمَهُ اللَّهُ وَسَقَاهُ» وهذا من فضل اللَّه عز وجل فالإنسان يعتريه النسيان، كما قال النبي صلى الله عليه وسلم: أَنَا بَشَرٌ مِثْلُكُمْ أَنْسَى كَمَا تَنْسَوْنَ

فالبشر من طبيعتهم النسيان، فإذا نسي وهو صائم في رمضان، أو في كفارة، أو في غيرهما، فأكل، أو شرب، أو تعاطى مفطراً آخر نسياناً، فصومه صحيح؛ لهذا الحديث الصحيح

وفي رواية أخرى عند الحاكم: «مَنْ أَفْطَرَ في رَمَضَانَ نَاسِيًا، فَلاَ قَضَاءَ عَلَيْهِ، وَلاَ كَفَّارَةَ» فلو جامع ناسياً، أو أكل ناسياً، أو شرب ناسياً؛ فإن صومه صحيح، ولا كفارة عليه، ولا عتق عليه، ولا قضاء عليه إذا كان ناسياً، واللَّه أعلم بالحقائق، فاللَّه يعلم بالحقيقة، واللَّه يعامل هذا على ما هو عليه من صدق أو كذب، لكن إن كان الإنسان صادقاً في أنه ناسٍ، فلا قضاء عليه، فصومه صحيح، أما إذا كان يكذب، فهذا أمره إلى اللَّه، لا تنفعه الفُتيا، ولو أفتاه رجل، إذا كان كاذباً، فعليه إثم ما فعله، لكن ما دام صادقاً في أنه ناسٍ فإن صومه صحيح.

والإنسان يُبتلى بالنسيان وهو معذور حتى في الصلاة التي هي أعظم الواجبات فقد ينسى، وقد يُسلم عن نقص، وقد يترك بعض الأركان، فيعمل ما شرعه اللَّه تعالى في الصلاة، إذا نسي ركعة أتى بركعة أخرى، وكمل صلاته بسجود السهو، إذا نسي ركناً أتى به، وإذا نسي واجباً سقط عنه، وسجد للسهو، فهكذا في الصوم، فالأمر ليس بخيار الإنسان، فإنه مخلوق على هذه الصفة ينسى، وقد نسي النبي صلى الله عليه وسلم وهو أفضل الخلق، وسها في الصلاة، – عليه الصلاة والسلام وهكذا بنو آدم، يُبتلون بالنسيان في الصلاة وغيرها، وقد بين الرسول صلى الله عليه وسلم أحكام النسيان في الصلاة، وهكذا في الصوم، أخبر صلى الله عليه وسلم أنه لا يضرّه أكله وشربه ناسياً، وهكذا جماعه وهكذا حجامته، وكل ما مرّ من المفطرات إذا فعله ناسياً ولم ينتبه إلا بعد ذلك، فصومه صحيح

الإفهام في شرح عمدة الأحكام ص ٣٩٢