Abd al-Rahman bin Abi Layla states: Sayyiduna Umar bin al-Khattab (may Allah be pleased with him) went out to look for the new crescent. A rider appeared before him, and Sayyiduna Umar (may Allah be pleased with him) asked: "Where are you coming from?" He replied: "From Syria." Sayyiduna Umar (may Allah be pleased with him) asked: "Have you seen the new crescent?" He replied: "Yes." Sayyiduna Umar (may Allah be pleased with him) said: "Allahu Akbar (Allah is the Greatest)." Then the believers met one another; after this the narrator mentioned the full hadith.
Abu Ya'la recorded it. Its chain contains a narrator, Jarir bin Ayyub al-Bajali, who is da'if (weak).
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الصيام / 4810