"The Messenger of Allah said: "The Messenger of Allah said: Do not fast before Ramadan. Fast when you see it and stop fasting when you see it, and if clouds prevent you from seeing it, then complete Thirty (Days)."' (Using translation from Nasāʾī 2130)
قَالَ رَسُولُ اللهِ ﷺ «لَا تَصُومُوا قَبْلَ رَمَضَانَ صُومُوا للِرُؤْيَة وَأَفْطِرُوا للِرُؤْيَة فَإِنْ حَالَتْ دُونَهُ غَيَايَةٌ فَأَكْمِلُوا ثَلَاثِينَ»