"The Messenger of Allah said: The month may be twenty-nine days or it may be thirty. When you see it, then stop fasting, and it is obscured from you (too cloudy), then complete the count."' (Using translation from Nasāʾī 2138)
قَالَ رَسُولُ اللهِ ﷺ «الشَّهْرُ يَكُونُ تِسْعًا وَعِشْرِينَ وَيَكُونُ ثَلَاثِينَ فَإِذَا رَأَيْتُمُوهُ فَصُومُوا وَإِذَا رَأَيْتُمُوهُ فَأَفْطِرُوا فَإِنْ غُمَّ عَلَيْكُمْ فَأَكْمِلُوا الْعِدَّةَ ثَلَاثِينَ»