An Arabi came to the Prophet ﷺ and said, "I have sighted the crescent," meaning the crescent of Ramadan.The Prophet ﷺ asked, "Do you bear witness that there is no god but Allah?"He replied, "Yes."The Prophet ﷺ asked, "Do you bear witness that Muhammad is the Messenger of Allah?"He replied, "Yes."The Prophet ﷺ said, "Bilal, announce to the people that they are to fast tomorrow."
جاء أعرابي إلى النبي ﷺ فقال: إني رأيت الهلال- يعني هلال رمضان- فقال: أتشهد أن لا إله إلا الله؟ قال: نعم، قال: أتشهد أن محمدا رسول الله؟ قال: نعم. قال: يا بلال، أذن في الناس أن يصوموا غدا.
Narrated by Abu Dawud (2340) and Tirmidhi (691), both from the hadith of Walid bin Abu Thawr, from Simak, from Ikrima, from Ibn Abbas, as mentioned. Zaida bin Qudama likewise narrated it from Simak, with a similar chain. Tirmidhi (691), Ibn Majah (1652), and Nasai (2113) narrated it through his route as well. Ibn Khuzayma (1923), Ibn Hibban (3446), and Hakim (1/424) all graded it sahih, all coming through this connected route. Hakim said, "Bukhari relied on the hadiths of Ikrima as evidence, and Muslim relied on the hadiths of Simak bin Harb and Hammad bin Salama as evidence, and this hadith is sahih though the two of them did not include it." Hammad bin Salama likewise narrated it from Simak with his chain, similarly. Hakim narrated it through his route (1/424), and from him Bayhaqi. Hazim bin Ibrahim likewise narrated it from Simak with his chain, similarly, and Tabarani narrated it through his route in Kabir (11/235).These companions of Simak narrated it from him as a connected chain, mentioning Ibn Abbas. Sufyan bin Uyayna narrated it from him, but his companions differed regarding him. Fadl bin Musa Sinani narrated it from Sufyan, from him, as a connected chain, and Nasai (2112) narrated it through his route, as did Bayhaqi (2124), who said, "It was likewise narrated from Abu Asim, from Thawri, as a connected chain, while others narrated it from Thawri as a disconnected chain (mursal)."I say, among those who narrated it as disconnected were Abu Dawud Tayalisi and Ibn Mubarak, both from Sufyan, from Simak, as disconnected, without mentioning Ibn Abbas. Nasai also narrated it through their route (2114, 2116).The ruling belongs to whoever narrated it connected, because it would not be proper for Ibn Abbas to say to Bilal, "Announce to the people..." Simak bin Harb, even though he was inconsistent in his narration from Ikrima, still has supporting evidence showing that he was not inconsistent in this particular case.Tirmidhi said, "The practice among most scholars is based on this hadith. They say that the testimony of a single man is accepted regarding fasting, and this is the view of Ibn Mubarak, Shafii, Ahmad, and the people of Kufa. Ishaq said, fasting should not begin except upon the testimony of two men. The scholars did not differ regarding breaking the fast, that only the testimony of two men is accepted for it." End of quote. See further in Minna Kubra (3/292–295).I add here that the later of Shafii's two positions is that two just witnesses are required, as found in Al-Umm. Rabi said, Shafii later said, "The sighting of the Ramadan crescent is not valid except with two witnesses." As for the Hanafis, they agreed with the majority that the sighting of the Ramadan crescent could be established by one just witness, but they specified this to cases where there was some obstruction in the sky such as clouds, dust, or the like. Otherwise, it would not be accepted except from a large group whose report produces certain knowledge. See Tarh Tathrib (4/115).