Mishkat al-Masabih #1887
mishkat_al_masabih:1887وَعَنِ ابْنِ عَبَّاسٍ قَالَ: " جَاءَ أَعْرَابِيٌّ إِلَى النَّبِيِّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ فَقَالَ: إِنِّي رَأَيْتُ الْهِلَالَ يَعْنِي هِلَالَ رَمَضَانَ فَقَالَ: «أَتَشْهَدُ أَنْ لَا إِلَهَ إِلَّا اللَّهُ؟» قَالَ: نَعَمْ قَالَ: «أَتَشْهَدُ أَنَّ مُحَمَّدًا رَسُولُ اللَّهِ؟» قَالَ: نَعَمْ. قَالَ: «يَا بِلَالُ أَذِّنْ فِي النَّاسِ أَن يَصُومُوا غَدا» . رَوَاهُ أَبُو دَاوُدَ وَالتِّرْمِذِيُّ وَالنَّسَائِيُّ وَابْنُ مَاجَهْ والدارمي
Ibn ‘Abbas told a desert Arab coming to the Prophet and saying he had seen the new moon, i.e. the new moon of Ramadan. He asked him whether he testified that there is no god but God and he replied that he did. He then asked if he testified that Muhammad is God’s messenger, and when he replied that he did he said, “Bilal, announce to the people that they must fast tomorrow." Abu Dawud, Tirmidhi, Nasa’i, Ibn Majah and Darimi transmitted it.