It wasnarrated from Abu Hurairah that the Messenger of Allah (ﷺ)said:
"When you see the new crescent then fast, and when you see itthenstop fasting. If it is cloudy then fast thirty days." (FR)
English reference (FR): Vol. 1, Book 7, Hadith 1655 (FR)
Arabic reference (FR): Book 7, Hadith 1724 (FR)