Narrated Aisha, Ummul Mu'minin: The Apostle of Allah (peace_be_upon_him) used to count the days in Sha'ban in a manner he did not count any other month; then he fasted when he sighted the new moon of Ramadan; but if the weather was cloudy he counted thirty days and then fasted. [+] [Abu Dawud 007:2318]