عَنْ قَيْسِ بْنِ طَلْقٍ عَنْ أَبِيهِ رَضِيَ اللَّهُ عَنْهُ قَالَ: قَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَآلِهِ وَسَلَّمَ: ((إِنَّ اللَّهَ عَزَّ وَجَلَّ جَعَلَ هَذِهِ الْأَهِلَّةَ مَوَاقِيتَ لِلنَّاسِ، صُومُوا لِرُؤْيَتِهِ وَأَفْطِرُوا لِرُؤْيَتِهِ، فَإِنْ غُمَّ عَلَيْكُمْ فَأَتِمُّوا الْعِدَّةَ))
It is narrated from Sayyiduna Taliq bin Ali, may Allah be pleased with him, that the Messenger of Allah, peace and blessings be upon him, said: Verily, Allah Almighty has made this moon a sign for the timings of people, so begin fasting by sighting the moon and end fasting by sighting it, and if the sky is cloudy, then complete the count to thirty.