The Prophet ﷺ said, "The month is like this, and this, and this," meaning thirty days. Then he said, "And like this, and this, and this," meaning twenty-nine days. He was saying that sometimes it is thirty days and sometimes twenty-nine.
حدثنا آدم حدثنا شعبة حدثنا جبلة بن سحيم سمعت
قال النبي ﷺ الشهر هكذا وهكذا وهكذا يعني ثلاثين ثم قال وهكذا وهكذا وهكذا يعني تسعا وعشرين يقول مرة ثلاثين ومرة تسعا وعشرين