Prohibition to fast before the beginning of Ramadan

the Messenger of Allah said: "Do not fast before Ramadan. Fast with its sighting, and break fast with its sighting, and if it is obscured from you due to a cloudy sky, then complete thirty days."

قَالَ رَسُولُ اللَّهِ ﷺ: «لاَ تَصُومُوا قَبْلَ رَمَضَانَ: صُومُوا لِرُؤْيَتِهِ، وَأَفْطِرُوا لِرُؤْيَتِهِ۔ فَإِنْ حَالَتْ دُونَهُ غَيَايَةٌ فَأَكْمِلُوا ثَلاَثِينَ يَوْمًا۔»