كتاب الصيام
Read the English translation first, with the original Arabic directly underneath.
It was narrated that Abu Hurairah said:
"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."'
الشَّهْرُ يَكُونُ تِسْعَةً وَعِشْرِينَ وَيَكُونُ ثَلاَثِينَ فَإِذَا رَأَيْتُمُوهُ فَصُومُوا وَإِذَا رَأَيْتُمُوهُ فَأَفْطِرُوا فَإِنْ غُمَّ عَلَيْكُمْ فَأَكْمِلُوا الْعِدَّةَ