Sayyiduna Abu Bakrah (may Allah be pleased with him) narrates: The Prophet (peace and blessings be upon him) said: "Every sacred month is not less than thirty days and thirty nights."
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 / 4821