• Difference among the jurists:
  The scholars disagreed over the ruling on fasting the thirtieth day of Shaʿbān when the crescent is hidden by cloud, dust, or the like.

Imām Ahmad, in the position most commonly ascribed to him, held that fasting on that day is obligatory. Al-Inṣāf states: “This is the authoritative view among the Hanbalīs. They defended it, composed treatises on it, rebutted the arguments of their opponents, and the explicit texts of Ahmad support it; it is one of his singular positions.”

They based their view on the narration recorded by al-Bukhārī (1900) and Muslim (1080) from Ibn ʿUmar, in which the Prophet ﷺ said, “When you see it, fast, and when you see it, break the fast; but if it is obscured from you, then calculate for it.” They explained “calculate for it” (fa-qdurū lah) to mean: restrict Shaʿbān, i.e., treat it as 29 days.

The other three Imāms, however, maintained that fasting on that day is not prescribed and that it is the very “day of doubt” the Prophet forbade. They cited the report transmitted by Abū Dāwūd (2334) and al-Tirmidhī (686) from ʿAmmār: “Whoever fasts the day about which there is doubt has disobeyed Abū al-Qāsim ﷺ.”

This is also one narration from Imām Ahmad. Al-Mughnī says: “According to another report from Ahmad, fasting it is not obligatory, and if a person does fast it, that fast does not count for Ramadan. This is the view of the majority of scholars.”

Shaykh al-Islām said: “Abstaining from fasting that day is the position explicitly affirmed by Ahmad, and the default in his words is non-obligation.” He added: “Fasting the day of doubt is to advance Ramadan by one day, and the Prophet ﷺ forbade that. The principles of the Sharia support this view more than the opposite, for what is doubtful in its obligation is not obligatory to perform; rather, the recommended course is to leave it.”

He further stated: “If one were to say that both options are permissible, while preferring not to fast, that would be more appropriate.”

Al-Furūʿ notes: “I have not found that Ahmad ever categorically declared it obligatory, nor that he commanded it.”