An Arabi came to the Prophet ﷺ and said, "I sighted the crescent moon tonight."The Prophet ﷺ asked him, "Do you bear witness that there is no god but Allah and that Muhammad is the Messenger of Allah?"He replied, "Yes."The Prophet ﷺ said, "Stand up, Bilal, and announce to the people that they should fast tomorrow."Abu Ali said, this is how Walid bin Abu Thawr and Hasan bin Ali narrated it. Hammad bin Salama also narrated it but did not mention Ibn Abbas, and his version says, "He called out to them to rise and to fast."
حدثنا عمرو بن عبد الله الأودي ومحمد بن إسمعيل قالا حدثنا أبو أسامة حدثنا زائدة بن قدامة حدثنا سماك بن حرب عن عكرمة
جاء أعرابي إلى النبي ﷺ فقال أبصرت الهلال الليلة فقال أتشهد أن لا إله إلا الله وأن محمدا رسول الله قال نعم قال قم يا بلال فأذن في الناس أن يصوموا غدا قال أبو علي هكذا رواية الوليد بن أبي ثور والحسن بن علي ورواه حماد بن سلمة فلم يذكر ابن عباس وقال فنادى أن يقوموا وأن يصوموا
[Its chain of transmission is daif. Abu Dawud narrated it in the Book of Sawm, chapter on the testimony of a single witness regarding the sighting of the crescent moon of Ramadan, hadith no. 2340, from the hadith of Zaida via this route. Ibn Khuzayma, Ibn Hibban, and Hakim graded it sahih. See hadith no. 171 regarding its defect.