Abu Bakr bin Nafi' (may Allah have mercy on him) narrates from his father, and he from Ibn Umar (may Allah be pleased with him), that the people looked for the new moon, and I informed the Messenger of Allah (peace and blessings be upon him) that I had seen it, so he (peace and blessings be upon him) fasted and ordered the people to fast.
Ali bin Umar al-Hafiz said: Marwan bin Muhammad is alone in narrating it from Ibn Wahb, and he is thiqah (trustworthy). This hadith is counted among the solitary narrations of Marwan bin Muhammad al-Dimashqi.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصيام / 7978