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.”
حَدَّثَنَا سُلَيْمَانُ بْنُ دَاوُدَ الْعَتَكِيُّ، حَدَّثَنَا حَمَّادٌ، حَدَّثَنَا أَيُّوبُ، عَنْ نَافِعٍ، عَنِ ابْنِ عُمَرَ، قَالَ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم " 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 .
AbuDaud
Fasting (Kitab Al-Siyam) • Hadith 2320