Masruq and Sayyiduna al-Bara' bin Azib (may Allah be pleased with him) narrate: The Prophet (peace and blessings be upon him) said: "Begin fasting upon sighting it and celebrate Eid al-Fitr upon sighting it, and if it is clouded over for you, complete the count of thirty." Then the Prophet (peace and blessings be upon him) indicated with his blessed hand and said: "The month is (sometimes) like this and like this," meaning that it is twenty-nine days.
Al-Tabarani recorded it in al-Mu'jam al-Kabir. Its chain contains a narrator, Ali bin Hashim bin al-Barid, who is saduq (truthful), but has Shi'i leanings.
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الصيام / 4804
Hadith Gradingمحدثین:إسنادہ حسن
Hadith Takhrij«أخرجه المعجم الكبير للطبراني برقم: 1175»