The people looked for the moon, so I informed the Messenger of Allah ﷺ that I had sighted it. He fasted and commanded the people to fast. (Using translation from Abū Dāʾūd 2342)  

«تَرَاءَى النَّاسُ الْهِلَالَ فَأَخْبَرْتُ رَسُولَ اللَّهِ ﷺ أَنِّي رَأَيْتُهُ فَصَامَ وَأَمَرَ النَّاسَ بِالصِّيَامِ»  

A bedouin came to the Prophet ﷺ and said: I have sighted the moon. Al-Hasan added in his version: that is, of Ramadan. He asked: Do you testify that there is no god but Allah? He replied: Yes. He again asked: Do you testify that Muhammad is the Messenger of Allah? He replied: Yes. and he testified that he had sighted the moon. He said: Bilal, announce to the people that they must fast tomorrow. (Using translation from Abū Dāʾūd 2340)   

جَاءَ أَعْرَابِيٌّ إِلَى النَّبِيِّ ﷺ وَقَالَ إِنِّي رَأَيْتُ الْهِلَالَ فَقَالَ «أَتَشْهَدُ أَنْ لَا إِلَهَ إِلَّا اللَّهُ وَأَنِّي رَسُولُ اللَّهِ؟» قَالَ نَعَمْ قَالَ «يَا بِلَالُ نَادِ فِي النَّاسِ فَلْيَصُومُوا غَدًا»