Narrated by:form Ibn 'Umar that the Prophet said
It was narrated form Ibn 'Umar that the Prophet said:"D not fast until you see it , and do not stop fasting until you see it, and if it is obscured from you (too cloudy), then work it out."
أَخْبَرَنَا عَمْرُو بْنُ عَلِيٍّ، قَالَ حَدَّثَنَا يَحْيَى، قَالَ حَدَّثَنَا عُبَيْدُ اللَّهِ، قَالَ حَدَّثَنِي نَافِعٌ، عَنِ ابْنِ عُمَرَ، عَنِ النَّبِيِّ صلى الله عليه وسلم قَالَ " لاَ تَصُومُوا حَتَّى تَرَوْهُ وَلاَ تُفْطِرُوا حَتَّى تَرَوْهُ فَإِنْ غُمَّ عَلَيْكُمْ فَاقْدُرُوا لَهُ " .
Nesai
The Book of Fasting • Hadith 2122