An Arabi came to the Prophet ﷺ and said, "I have sighted the crescent moon."The Prophet ﷺ asked him, "Do you bear witness that there is no god but Allah and that Muhammad is His servant and messenger?"He replied, "Yes."So the Prophet ﷺ called out for the people to begin fasting.
أخبرنا محمد بن عبد العزيز بن أبي رزمة قال أنبأنا الفضل بن موسى عن سفيان عن سماك عن عكرمة
جاء أعرابي إلى النبي ﷺ فقال رأيت الهلال فقال أتشهد أن لا إله إلا الله وأن محمدا عبده ورسوله قال نعم فنادى النبي ﷺ أن صوموا
Its isnad is daif. Abu Dawud narrated it in the Book of Fasting, chapter on the testimony of one person regarding the sighting of the crescent moon of Ramadan, no. 2340, and Tirmidhi, no. 691, and Ibn Majah, no. 1652, through the hadith of Simak with the same wording. It is also found in Sunan al-Kubra, no. 2423, and Ibn Khuzayma, Ibn Hibban, and Hakim graded it sahih.Simak's transmission from Ikrima is daif, as mentioned earlier at no. 326, as I established in Nayl Maqsud, no. 68. May Allah make its printing easy for us.