This event is confirmed by sighting the new moon, even if it is seen by only one just person, or by the passage of thirty days in the immediately preceding month of Sha’ban.
Ibn ‘Umar said: “The people were looking for the new moon and when I reported to the Messenger of Allah that I had seen it, he fasted and ordered the people to fast.”
Commenting on these reports, at-Tirmizhi states: “Most knowledgeable people act in accordance with these reports. They say that it is correct to accept the evidence of one person to determine the beginning of the fast. This is the opinion of Ibn al-Mubarak, ash-Shaf’i, and Ahmad. An-Nawawi says that it is the soundest opinion. Concerning the new moon of Shawwal [which signifies the end of the fast], it is confirmed by completing thirty days of Ramadan, and most jurists state that the new moon must have been reported by at least two just witnesses. However, Abu Thaur does not distinguish between the new moon of Shawwal and the new moon of Ramadan. In both cases, he accepts the evidence of only one just witness.”
Ash-Shaukani observes: “If there is nothing authentic recorded that states that one may only accept two witnesses for the end of the month, then it is apparent, by analogy, that one witness is sufficient, as it is sufficient for the beginning of the month.