حَدَّثَنَا مُحَمَّدُ بْنُ بَكَّارِ بْنِ الرَّيَّانِ، حَدَّثَنَا الْوَلِيدُ، - يَعْنِي ابْنَ أَبِي ثَوْرٍ ح وَحَدَّثَنَا الْحَسَنُ بْنُ عَلِيٍّ، حَدَّثَنَا الْحُسَيْنُ، - يَعْنِي الْجُعْفِيَّ - عَنْ زَائِدَةَ، - الْمَعْنَى - عَنْ سِمَاكٍ، عَنْ عِكْرِمَةَ، عَنِ ابْنِ عَبَّاسٍ، قَالَ جَاءَ أَعْرَابِيٌّ إِلَى النَّبِيِّ صلى الله عليه وسلم فَقَالَ إِنِّي رَأَيْتُ الْهِلاَلَ - قَالَ الْحَسَنُ فِي حَدِيثِهِ يَعْنِي رَمَضَانَ - فَقَالَ ‏"‏ أَتَشْهَدُ أَنْ لاَ إِلَهَ إِلاَّ اللَّهُ ‏"‏ ‏.‏ قَالَ نَعَمْ ‏.‏ قَالَ ‏"‏ أَتَشْهَدُ أَنَّ مُحَمَّدًا رَسُولُ اللَّهِ ‏"‏ ‏.‏ قَالَ نَعَمْ ‏.‏ قَالَ ‏"‏ يَا بِلاَلُ أَذِّنْ فِي النَّاسِ فَلْيَصُومُوا غَدًا ‏"‏ ‏.‏

Narrated Abdullah ibn Abbas: A bedouin came to the Prophet (PBUH) 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. Translation Not Available

Book Ref: Sunan Abi Dawud Book 14 Hadith 2340
Web Ref:  Sunan Abi Dawud Book 13 Hadith 2333