Ubaidullah bin 'Abdullah bin Abi Thaur عبيد الله بن عبد الله بن أبي ثور · The Book of Fasting

"The Messenger of Allah said: 'D not anticipate the month until you complete the number, or you see the crescent. Then fast, and do not stop fasting until you see the crescent, or your complete thirty days."' (Sahih) Al-Hajjaj bin Artah reported it in a Mursal from.