"A Bedouin come to the Prophet and said; 'I have sighted the crescent tonight.' He said: 'Do you bear witness that there is none worthy of worship except Allah, and that Messenger?' He said: 'Yes.' He said: 'O Bilal, announce to the people that they should fast tomorrow. "' (Using translation from Nasāʾī 2113)  

جَاءَ أَعْرَابِيٌّ إِلَى النَّبِيِّ ﷺ فَقَالَ أَبْصَرْتُ الْهِلَالَ اللَّيْلَةَ قَالَ «أَتَشْهَدُ أَنْ لَا إِلَهَ إِلَّا اللهُ وَأَنَّ مُحَمَّدًا عَبْدُهُ وَرَسُولُهُ؟» قَالَ نَعَمْ قَالَ «يَا بِلَالُ أَذِّنْ فِي النَّاسِ فَلْيَصُومُوا غَدًا»