Musnad Abu Ya'la al-Mawsili 6:135

Muhammad ibn Abd Allah ibn Numayr narrated to us, Muhammad ibn Bishr narrated to us, from Isma'il ibn Abi Khalid, from Muhammad ibn Sa'd, from his father, who said: The Messenger of Allah (ﷺ) said: "The month is like this, and like this, and like this," and he withheld a finger in the third [time].