"Fast when you see it, and stop fasting when you see it, and if clouds prevent you from seeing it, then complete the number, and do not fast ahead of Ramadan." (Using translation from Nasāʾī 2129)
عَنْ رَسُولِ اللهِ ﷺ قَالَ «صُومُوا لِرُؤْيَتِهِ وَأَفْطِرُوا لِرُؤْيَتِهِ فَإِنْ حَالَ بَيْنَكُمْ وَبَيْنَهُ سَحَابٌ فَكَمِّلُوا الْعِدَّةَ وَلَا تَسْتَقْبِلُوا الشَّهْرَ اسْتِقْبَالًا»