Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him) says: The fasts are to be started upon sighting the new crescent and kept until it is sighted again; if it is hidden from you, then (the fasts are to be kept for) thirty days.
Al-Tabarani recorded it in al-Mu'jam al-Kabir, and its narrators are the narrators of the Sahih.
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الصيام / 4809
Hadith Gradingمحدثین:إسنادہ صحیح
Hadith Takhrij«اخرجه الطبرانى فى المعجم الكبير (9563)»