Hadith 2325
Narrated Aishah, Ummul Muminin: The Messenger of Allah ﷺ 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.
Hadith 2326
Narrated Hudhayfah: The Prophet ﷺ said: Do not fast (for Ramadan) before the coming of the month until you sight the moon or complete the number (of thirty days); then fast until you sight the moon or complete the number (of thirty days).