Harmalah ibn Yahya narrated to me: Ibn Wahb informed us: Yunus informed me, from Ibn Shihab, who said: Salim ibn Abdullah narrated to me that Abdullah ibn Umar — may Allah be pleased with them both — said: I heard the Messenger of Allah, peace and blessings be upon him, say: "When you see it (the crescent moon), fast, and when you see it, break your fast. And if it is obscured from you, then estimate it."