The Book of Prayers (Kitab Al-Salat)

Muslim :: Book 4 : Hadith 1809

Abu Basra Ghifari reported: The Messenger of Allah (may peace be upon him) led us in the 'Asr prayer at (the place known as) Mukhammas, and then said: This prayer was presented to those gone before you, but they lost it, and he who guards it has two rewards in store for him. And no prayer is valid after till the onlooker appears (by onlooker is meant the evening star).