Narrated Ibn `Umar: The Prophet said, "We are an illiterate nation; we neither write, nor know accounts. The month is like this and this, i.e. sometimes of 29 days and sometimes of thirty days."
Hadith Referenceصحيح البخاري / كتاب الصوم / 1913
Hadith Gradingمحدثین:أحاديث صحيح البخاريّ كلّها صحيحة