Yahya ibn Yahya narrated to us, Ibrahim ibn Sa'd informed us, from Ibn Shihab, from Sa'id ibn al-Musayyab, from Abu Hurayrah — may Allah be pleased with him — who said: The Messenger of Allah, peace and blessings be upon him, said: "When you see the crescent, fast, and when you see it, break your fast. But if it is obscured from you, then fast thirty days."