When is fasting obligatory based on sighting the new moon (Hilal) of Ramadan?
General Chapter
Al-Mughni
Book of Fasting
Primary text
Fasting becomes obligatory upon the sighting of the crescent moon by a single individual, whether that person is just or unjust, whether their testimony is accepted by the judge or rejected. This is the view of Malik, al-Layth, al-Shafi'i, the proponents of the opinion of Abu Hanifa, and Ibn al-Mundhir. The basis is that one is certain the month has begun, obligating the fast, as in the case where the judge rules based on a single witness, or when one's own sighting confirms it.
Supporting text
Ata and Ishaq hold that fasting is not obligatory based on a single witness. A narration from Ahmad suggests two witnesses are preferred. The argument against a single witness is that sighting is a matter that should be confirmed by the populace, similar to the 29th day of Sha'ban being judged based on the majority.