Sahih Bukhari, Chapter: Times of the Prayers

We were with the Prophet on a full moon night. He looked at the moon and said, "You will certainly see your Lord as you see this moon, and there will be no trouble in seeing Him. So if you can avoid missing (through sleep, business, etc.) a prayer before the rising of the sun (Fajr) and before its setting ('Asr) you must do so. He (the Prophet ) then recited the following verse: And celebrate the praises Of Your Lord before The rising of the sun And before (its) setting." (50.39)