Ibn ‘Umar reported the Apostle of Allaah ﷺ as saying “The month consists of twenty nine days, but do not fast till you sight it (the moon) and do not break your fast till you sight it. If the weather is cloudy, calculate it thirty days. When the twenty-ninth of Sha’ban came, Ibn ‘Umar would send someone (who tried) to sight the moon for him. If it was sighted then well and good, in case it was not sighted and there was no cloud and dust before him (on the horizon) he would not keep fast the next day. If there appeared (on the horizon) before him cloud or dust, he would fast the following day. Ibn ‘Umar would end his fasting alone with the people and did not follow this calculation.”  

قَالَ رَسُولُ اللَّهِ ﷺ الشَّهْرُ تِسْعٌ وَعِشْرُونَ فَلاَ تَصُومُوا حَتَّى تَرَوْهُ وَلاَ تُفْطِرُوا حَتَّى تَرَوْهُ فَإِنْ غُمَّ عَلَيْكُمْ فَاقْدُرُوا لَهُ ثَلاَثِينَ قَالَ فَكَانَ ابْنُ عُمَرَ إِذَا كَانَ شَعْبَانُ تِسْعًا وَعِشْرِينَ نُظِرَ لَهُ فَإِنْ رُؤِيَ فَذَاكَ وَإِنْ لَمْ يُرَ وَلَمْ يَحُلْ دُونَ مَنْظَرِهِ سَحَابٌ وَلاَ قَتَرَةٌ أَصْبَحَ مُفْطِرًا فَإِنْ حَالَ دُونَ مَنْظَرِهِ سَحَابٌ أَوْ قَتَرَةٌ أَصْبَحَ صَائِمًا قَالَ فَكَانَ ابْنُ عُمَرَ يُفْطِرُ مَعَ النَّاسِ وَلاَ يَأْخُذُ بِهَذَا الْحِسَابِ  

[Machine] The Messenger of Allah ﷺ said, "Indeed, the month is twenty-nine days, so do not fast until you see it, and do not break your fast until you see it. If it is cloudy and unclear to you, then estimate it." Hammam narrated from Ayub who said, "Whenever Ibn Umar would finish the month of Sha'ban as twenty-nine days, he would look for the moon. If he saw it, he would fast, and if he did not see it, and there were no clouds or fog obstructing his view, then he would break his fast. And he would break his fast with the people and not follow this calculation." Ibn 'Awn also said, "I mentioned the actions of Ibn 'Umar to Muhammad bin Sirin, and it did not please him."  

قَالَ رَسُولُ اللهِ ﷺ إِنَّمَا الشَّهْرُ تِسْعٌ وَعِشْرُونَ فَلَا تَصُومُوا حَتَّى تَرَوْهُ وَلَا تُفْطِرُوا حَتَّى تَرَوْهُ فَإِنْ غُمَّ عَلَيْكُمْ فَاقْدُرُوا لَهُ زَادَ حَمَّادٌ فِي رِوَايَتِهِ عَنْ أَيُّوبَ قَالَ نَافِعٌ كَانَ ابْنُ عُمَرَ إِذَا مَضَى مِنْ شَعْبَانَ تِسْعٌ وَعِشْرُونَ نَظَرَ لَهُ فَإِنْ رُئِيَ فَذَاكَ وَإِنْ لَمْ يَرَ وَلَمْ يَحُلْ دُونَ مَنْظَرِهِ سَحَابٌ وَلَا قَتَرَةٌ أَصْبَحَ مُفْطِرًا وَإِنْ حَالَ دُونَ مَنْظَرِهِ سَحَابٌ أَوْ قَتَرَةٌ أَصْبَحَ صَائِمًا وَكَانَ يُفْطِرُ مَعَ النَّاسِ وَلَا يَأْخُذُ بِهَذَا الْحِسَابِ قَالَ وَقَالَ ابْنُ عَوْنٍ ذَكَرْتُ فِعْلَ ابْنِ عُمَرَ لِمُحَمَّدِ بْنِ سِيرِينَ فَلَمْ يُعْجِبْهُ