The Messenger of Allah ﷺ said, "The month is twenty-nine days. Do not fast until you see it, and do not break your fast until you see it. If it is obscured from you, then complete thirty days."When the twenty-ninth night of Shaban came, Ibn Umar would look for the moon. If it was sighted, that settled the matter. If it was not sighted and there were no clouds or haze blocking the view, he would begin the next day not fasting. But if clouds or haze blocked the view, he would begin the day fasting.Yet Ibn Umar would break the fast along with the people and would not act on this calculation of his own.
قال رسول الله ﷺ: الشهر تسع وعشرون فلا تصوموا حتى ترواه، ولا تفطروا حتى ترواه، فإن غم عليكم فاقدروا له ثلاثين. قال: فكان ابن عمر إذا كان شعبان تسعا وعشرين نظر له، فإن رؤي فذاك، وإن لم ير ولم يحل دون نظره سحاب ولا قترة أصبح مفطرا، فإن حال دون منظره سحاب أو قترة أصبح صائما. قال: فكان ابن عمر يفطر مع الناس، ولا يأخذ بهذا الحساب.
Abu Dawud (2320) narrated it from Dawud bin Sulayman Ataki, who said, Hammad told us, Ayub told us, from Nafi, from Ibn Umar, and he related it. Its chain of transmission is sahih. The marfu part of it is found in the Sahihayn as mentioned before, except that they did not mention the story of Ibn Umar. Bayhaqi (4/204) reported it through another route from Ayub, and said, Ibn Awn said, "I mentioned Ibn Umar's action to Muhammad bin Sirin, and he did not approve of it." He also said, "Muslim (1080:6) reported it from Zuhayr bin Harb, from Ismail bin Ulaya (from Ayub) without Ibn Umar's action." End of quote.As for the statement, "Ibn Umar used to break his fast with the people, and he did not rely on this calculation," it means that he used to do this practice in the month of Shaban as a precaution for the fast, but he did not rely on this calculation in the month of Ramadan, and he would not break his fast except with the people.Qatarah means the haze in the air that obstructs the sight from seeing the crescent moon. This was explained by Abu Sulayman Khattabi.Umar bin Abdul-Aziz wrote to the people of Basra, "We have received from the Messenger of Allah ﷺ something similar to the hadith of Ibn Umar, from the Prophet ﷺ," and he added, "The best estimate for it is that when we see the crescent of Shaban on such and such a day, then the fast, Allah willing, will be on such and such a day, unless you see the crescent before that."Abu Dawud (2321) narrated it from Humayd bin Masada, who said, Abdul-Wahhab told us, Ayub told me, he said, Umar bin Abdul-Aziz wrote, and he related it. Its narrators are trustworthy up to Umar bin Abdul-Aziz.Munziri said in his Mukhtasar, "This statement of Umar bin Abdul-Aziz is confirmed by the established narrations from the Messenger of Allah ﷺ."Bayhaqi (4/205) said, "What indicates the correctness of what Umar bin Abdul-Aziz mentioned is the rest of the narrations from the Prophet ﷺ on this subject, among them the hadith of Ibn Umar."They mean the marfu hadith of Ibn Umar, which is his saying, "The month is twenty-nine days, so do not fast until you see it, and do not break your fast until you see it, and if it is obscured from you, then estimate it as thirty."This statement of Umar bin Abdul-Aziz is the view held by most scholars, among them Abu Hanifa, Malik, Shafii, and Ahmad according to one narration, and it is the ruling adopted by the Permanent Committee's fatwa.