Abu Huraira reported Allah's Messenger (ﷺ) as saying:Whenever you sight the new moon (of the month of Ramadan) observe fast. and when you sight it (the new moon of Shawwal) break it, and if the sky is cloudy for you, then observe fast for thirty days

Abu Huraira reported Allah's Messenger (ﷺ) as saying:Observe fast on sighting it (the new moon) and break (fast) on sighting it (the new moon), but if the sky is cloudy for you, then complete the number (of thirty)

Abu Huraira reported Allah's Messenger (ﷺ) as saying:Observe fast on sighting it (the new moon) and break it on sighting it. But if (due to clouds) the actual position of the month is concealed from you, you should then count thirty (days)

Abu Huraira (Allah be pleased with him) narrated that the Messenger of Allah (may peace he upon him) made a mention of the new moon and (in this connection) said:Observe fast when you see it (the new moon) and break fast when you see it (the new moon of Shawwal), but when (the actual position of the month is) concealed from you (on account of cloudy sky), then count thirty days