The Prophet ﷺ said, "We are an unlettered nation. We neither calculate nor write. The month is like this, and like this, and like this," then he reduced one finger on the third time.
حدثنا عبيدة بن حميد حدثني الأسود بن قيس عن سعيد بن عمرو القرشي أن
عن النبي ﷺ أنه قال إنا أمة أمية لا نحسب ولا نكتب وإن الشهر هكذا وهكذا وهكذا ثم نقص واحدة في الثالثة
Its isnad is sahih. It has already been mentioned in similar wording through the narration of Aswad bin Qays from Saeed bin Amr [5017, 5137], and through the narration of Ishaq bin Saeed bin Amr from his father [6041].