Fasting The Day of Doubt (Yâum As-Shák)

Excerpts from the ‘Jurisprudence of Worship’
By Shaykh Muhammad ibn Saalih ibn Uthaymeen رحمه الله تعالى

Question: Oh Noble Shaykh, What is the ruling of fasting the day doubt (Yâum As-Shák)?

Answer:
The closest position (to correctness) is that fasting the day of doubt is certainly forbidden (haraam).
By the statement of narrated by ‘Āmir ibn Yāsir (from the early believers may Allāh be pleased with all of them) رضى الله عنه:
Whoever fasts a day that he is doubtful in (he is not certain if it is 30th of Sh’abān or if it is the 1st day of Ramadān), verily he has disobeyed Aba Al-Qasim (the Prophet Muhammad) ﷺ.

Therefore, the one who fasts on the day of doubt is overstepping the boundaries of Allāh عز وجل. For verily the boundaries set by Allāh are that he should not observe the fast of Ramadān except by the sighting of the new moon (of the month of Ramadan) or the completion of 30 days in the month of Sh’abān.

Regarding this the Prophet Muhammad ﷺ said:
“None of you should fast a day or two before the month of Ramadan unless he has the habit of fasting (Nawafil) (and if his fasting coincides with that day) then he can fast that day.”¹

As for a person under the authority of the Muslims, he must follow that authority. And if it is confirmed by that authority, the affair of the beginning of the month (Ramadān), then he should fast following the Muslims. And if it is not confirmed by the local authority, then he should not fast. (This is in the case that he has not seen the new moon himself as there is a specific ruling pertaining to that).

¹Related by Bukhari- The Book of Fasting [Number 1914] and related by Muslim-The Book of Fasting [Number 1082]

Jurisprudence of Worship- Fatwa For Sâum (Fasting) (Pg.266-267)

Translated by: Abu Uwāis, Muhammad Abdullahi Elmi