"Do not fast until you see the crescent, and do not stop fasting until you see it, and if it is obscured from you (too cloudy), then work it out."

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