Benefit: Ramaḍān - The Validity of the Fast of the One Who Eats or Drinks When He Ought to Be Fasting
In the Name of Allāh, the Ever Merciful, the Bestower of Mercy
Faṭwá Series for Ramaḍān 2016 - featuring selected faṭāwá by Shaykh Aḥmad ibn Yaḥyá al-Najmī (رحمه الله).
[A]: If it was unclear that it was the time of dawn, so he ate or drank thinking that it wasn't, then his fast is valid and he doesn't have to make it up. As for if it was very clear that he ate and drank after dawn or before sunset, then upon him is to make it up.
Shaykh Aḥmad ibn Yaḥyá al-Najmī (رحمه الله).
Source: Fatāwá al-Ṣiyām pg 40.
Translated by: Musa Shaleem Mohammed