Messenger of Allah ﷺ mentioned Ramadan and said, "Do not fast unless you see the crescent (of Ramadan), and do not give up fasting till you see the crescent (of Shawwal), but if the sky is overcast (if you cannot see it), then act on estimation (i.e. count Sha'ban as 30 days).  

أَنَّ رَسُولَ اللَّهِ ﷺ ذَكَرَ رَمَضَانَ فَقَالَ لاَ تَصُومُوا حَتَّى تَرَوُا الْهِلاَلَ وَلاَ تُفْطِرُوا حَتَّى تَرَوْهُ فَإِنْ غُمَّ عَلَيْكُمْ فَاقْدُرُوا لَهُ  

Messenger of Allah ﷺ said, "The month (can be) 29 nights (i.e. days), and do not fast till you see the moon, and if the sky is overcast, then complete Sha'ban as thirty days."  

أَنَّ رَسُولَ اللَّهِ ﷺ قَالَ الشَّهْرُ تِسْعٌ وَعِشْرُونَ لَيْلَةً فَلاَ تَصُومُوا حَتَّى تَرَوْهُ فَإِنْ غُمَّ عَلَيْكُمْ فَأَكْمِلُوا الْعِدَّةَ ثَلاَثِينَ  

The Prophet ﷺ said, "The month is like this and this," (at the same time he showed the fingers of both his hands thrice) and left out one thumb on the third time.  

قَالَ النَّبِيُّ ﷺ الشَّهْرُ هَكَذَا وَهَكَذَا وَخَنَسَ الإِبْهَامَ فِي الثَّالِثَةِ  

that the Prophet ﷺ said or he said Abū al-Qasim said, "˹Start˺ fasting ˹the month˺ upon seeing it (the moon), and break ˹fasting the month˺ upon seeing it. If it is hidden for you (as a result of an overcast at the start of the month), then complete thirty days of Shaʿbān."  

قَالَ النَّبِيُّ ﷺ أَوْ قَالَ قَالَ أَبُو الْقَاسِمِ ﷺ «صُومُوا لِرُؤْيَتِهِ وَأَفْطِرُوا لِرُؤْيَتِهِ فَإِنْ غُبِّيَ عَلَيْكُمْ فَأَكْمِلُوا عِدَّةَ شَعْبَانَ ثَلاَثِينَ۔»  

The Prophet ﷺ vowed to keep aloof from his wives for a period of one month, and after the completion of 29 days he went either in the morning or in the afternoon to his wives. Someone said to him "You vowed that you would not go to your wives for one month." He replied, "The month is of 29 days."  

أَنَّ النَّبِيَّ ﷺ آلَى مِنْ نِسَائِهِ شَهْرًا فَلَمَّا مَضَى تِسْعَةٌ وَعِشْرُونَ يَوْمًا غَدَا أَوْ رَاحَ فَقِيلَ لَهُ إِنَّكَ حَلَفْتَ أَنْ لاَ تَدْخُلَ شَهْرًا فَقَالَ إِنَّ الشَّهْرَ يَكُونُ تِسْعَةً وَعِشْرِينَ يَوْمًا  

Messenger of Allah ﷺ vowed to keep aloof from his wives for one month, and he had dislocation of his leg. So, he stayed in a Mashruba for 29 nights and then came down. Some people said, "O Messenger of Allah ﷺ! You vowed to stay aloof for one month," He replied, "The month is of 29 days."  

آلَى رَسُولُ اللَّهِ ﷺ مِنْ نِسَائِهِ وَكَانَتِ انْفَكَّتْ رِجْلُهُ فَأَقَامَ فِي مَشْرُبَةٍ تِسْعًا وَعِشْرِينَ لَيْلَةً ثُمَّ نَزَلَ فَقَالُوا يَا رَسُولَ اللَّهِ آلَيْتَ شَهْرًا فَقَالَ إِنَّ الشَّهْرَ يَكُونُ تِسْعًا وَعِشْرِينَ