'Abdur-Rahman bin Zaid bin Al-Khattab addressed the people on the day concerning which there was doubt (as to whether the month had begun) and said: "I sat with the Companions of the Messenger of Allah and asked them, and they a narrated that the Messenger of Allah said: 'Fast when you see it and stop fasting when you see it, and perform the rites on that basis. If it is obscured, then complete thirty days, and if two witnesses testify then fast and stop fasting." (Using translation from Nasāʾī 2116)   

أَلَا إِنِّي قَدْ جَالَسْتُ أَصْحَابَ رَسُولِ اللهِ ﷺ وَسَأَلْتُهُمْ أَلَا وَإِنَّهُمْ حَدَّثُونِي أَنَّ رَسُولَ اللهِ ﷺ قَالَ صُومُوا لِرُؤْيَتِهِ وَأَفْطِرُوا لِرُؤْيَتِهِ وَأَنْسِكُوا لَهَا فَإِنْ غُمَّ عَلَيْكُمْفَأَتِمُّوا ثَلَاثِينَ وَإِنْ شَهِدَ شَاهِدَانِ مُسْلِمَانِ فَصُومُوا وَأَفْطِرُوا