The Prophet ﷺ said: Do not fast (for Ramadan) before the coming of the month until you sight the moon or complete the number (of thirty days); then fast until you sight the moon or complete the number (of thirty days). (Using translation from Abū Dāʾūd 2326)  

عَنْ رَسُولِ اللهِ ﷺ قَالَ «لَا تَقَدَّمُوا الشَّهْرَ حَتَّى تَرَوُا الْهِلَالَ أَوْ تُكْمِلُوا الْعِدَّةَ ثُمَّ صُومُوا حَتَّى تَرَوُا الْهِلَالَ أَوْ تُكْمِلُوا الْعِدَّةَ قَبْلَهُ»  

"The Messenger of Allah said: 'D not anticipate the month until you complete the number, or you see the crescent. Then fast, and do not stop fasting until you see the crescent, or your complete thirty days."' (Sahih) Al-Hajjaj bin Artah reported it in a Mursal from. (Using translation from Nasāʾī 2127)  

عَنْ بَعْضِ أَصْحَابِ النَّبِيِّ ﷺ قَالَ قَالَ رَسُولُ اللهِ ﷺ «لَا تَقَدَّمُوا الشَّهْرَ حَتَّى تُكْمِلُوا الْعِدَّةَ أَوْ تَرَوُا الْهِلَالَ ثُمَّ صُومُوا فَلَا تُفْطِرُوا حَتَّى تُكْمِلُوا الْعِدَّةَ أَوْ تَرَوُا الْهِلَالَ» أَرْسَلَهُ الْحَجَّاجُ بْنُ أَرْطَاةَ  

"The Messenger of Allah said: 'When you see the crescent then fast, and when you see it, then stop fasting. If it is too cloudy then complete Shaban as thirty days, unless you see the crescent before that, then fast Ramadan as thirty days, unless you see the new crescent before that."' (Using translation from Nasāʾī 2128)  

قَالَ رَسُولُ اللهِ ﷺ «إِذَا رَأَيْتُمُ الْهِلَالَ فَصُومُوا وَإِذَا رَأَيْتُمُوهُ فَأَفْطِرُوا فَإِنْ غُمَّ عَلَيْكُمْ فَأَتِمُّوا ثَلَاثِينَ أَتِمُّوا شَعْبَانَ ثَلَاثِينَ إِلَّا أَنْ تَرَوُا الْهِلَالَ قَبْلَ ذَلِكَ ثُمَّ صُومُوا رَمَضَانَ ثَلَاثِينَ إِلَّا أَنْ تَرَوُا الْهِلَالَ قَبْلَ ذَلِكَ»  

"Fast when you see it, and stop fasting when you see it, and if clouds prevent you from seeing it, then complete the number, and do not fast ahead of Ramadan." (Using translation from Nasāʾī 2129)  

عَنْ رَسُولِ اللهِ ﷺ قَالَ «صُومُوا لِرُؤْيَتِهِ وَأَفْطِرُوا لِرُؤْيَتِهِ فَإِنْ حَالَ بَيْنَكُمْ وَبَيْنَهُ سَحَابٌ فَكَمِّلُوا الْعِدَّةَ وَلَا تَسْتَقْبِلُوا الشَّهْرَ اسْتِقْبَالًا»  

"The Messenger of Allah said: "The Messenger of Allah said: Do not fast before Ramadan. Fast when you see it and stop fasting when you see it, and if clouds prevent you from seeing it, then complete Thirty (Days)."' (Using translation from Nasāʾī 2130)  

قَالَ رَسُولُ اللهِ ﷺ «لَا تَصُومُوا قَبْلَ رَمَضَانَ صُومُوا للِرُؤْيَة وَأَفْطِرُوا للِرُؤْيَة فَإِنْ حَالَتْ دُونَهُ غَيَايَةٌ فَأَكْمِلُوا ثَلَاثِينَ»