"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»