Fiqh-us-Sunnah - 1.84

Hadith 1.84.1

The time for the afternoon prayer ('asr)

This prayer begins in the afternoon when the shadow of an object is of the same length as the object itself, and continues until the sun sets. Abu Hurairah reported that the Prophet, upon whom be peace, said, "Whoever catches one rak'ah of the afternoon prayer before the sun sets and then prays the remainder of the prayer after the sun has set has not missed the afternoon prayer."
The best and most preferred time to pray the afternoon prayer ends when the sun becomes yellowish on the horizon. This is implied by the preceding hadith of Jabir and 'Abdullah ibn 'Umar. To delay the prayer until the sun becomes yellowish, although it is permissiable, is greatly disliked, unless there is some need to do so.
Anas reported that he heard the Prophet, upon whom be peace, say, "The following is the prayer of the hypocrite: he waits until the sun is between the horns of Satan, then he gets up and prays four quick rak'ah, and he does not remember Allah therein save a little bit."
(Related by "the group," except for al-Bukhari and Ibn Majah.) Says an-Nawawi in his commentary on Sahih Muslim, "Our companions (the Shafiyyah) hold that the afternoon prayer time can be divided into five categories: the most virtuous time, the preferred time, the allowable time in which there is no disliked aspect, the allowable time that contains some aspect of dislike, and the time that is due to some excuse or necessity. The most virtuous time is at the beginning of the permissible time. The preferred time is until the shadow of an object is twice the length of the object itself. The permissible time without any aspect of dislike is from the time the sun becomes yellowish. The permissible time with some aspect of dislike is from the time the sun becomes yellowish until the setting of the sun. The time of excuse or necessity begins, in fact, at the time of the noon prayer for one who is to combine the noon and afternoon prayers, due to travelling or rain. If the afternoon prayer is made during any of those times, it has been fulfilled properly. If all of those times pass and the sun has set, then one must make up the prayer."
On a cloudy day, it should be prayed earlier in its time.
Buraidah al-Aslami reported, "We were with the Messenger of Allah, upon whom be peace, during a battle and he said, "Hasten in praying on a cloudy day, for one who misses the afternoon prayer has destroyed all of his works." (Related by Ahmad and Ibn Majah.) Of the subjecat, Ibn al-Qayyim says, "Leaving the prayer is of two types: leaving it completely and never praying it (which destroys all of one's deeds), and leaving it during a particular day, which destroys all of the deeds of that day."