His, peace and blessings of Allah be upon him, saying, “Journey [to Allah] in the beginning of the day, the end of the day, and a portion of the latter part of the night” has the meaning of his saying in other narrations, “Seek help in this journeying [to Allah] at the beginning of the day, at the end of the day and a portion of the latter part of the night.”
The meaning of this is that these three periods are times of journeying to Allah through performing actions of obedience. Allah, Exalted is He, has mentioned these times in His sayings, “Remember the name of your Lord [in prayer] the morning and evening, and during the night prostrate to Him and exalt Him a long [part of the] night.” (Surah al-Insan 76: 25-26) “Praise your Lord before the rising of the sun and before its setting; and during periods of the night [exalt Him] and at the ends of the day, that you may be satisfied.” (Surah Ta Ha 20:130) “And praise your Lord before the rising of its sun and before its setting. And [in part] the night exalt Him and after prostration.” (Surah Qaf 50: 39-40)
Allah, Most High, mentions the remembrance of Him at the two ends of the day in numerous places in His Book such as, “O you who believe! Remember Allah with much remembrance and glorify Him morning and evening.” (Surah al-Ahzab 33: 41-42) “Praise your Lord in the evening and in the morning.” (Surah Ghafir 40:55) “Do not turn away those who call upon their Lord morning and afternoon.” (Surah al-Anam 6:52) He said concerning the temperance of Zakariyah, peace be upon him, “…and signified to them: Glorify (your Lord) at morning and fall of night.” (Surah Maryam 19:11) And, “…glorify (Him) at the fall of night and in the early hours.” (Surah Ali Imran 3:41)
Out of these three times there are two which are at the beginning of the day and the end of the day. At these two times one finds both obligatory and optional actions to do. The obligatory actions are the prayers of Fajr and Asr and these are the two best of the five daily prayers. These are the prayers prayed at ‘the two cool periods”‘and whoever preserves these two prayers shall enter Paradise. (Bukhari and Muslim) It is said about both these prayers that they are the ‘Middle Prayer’. (Bukhari and Muslim) As for the optional deed then it is to remember Allah after the Fajr prayer until the sun rises and after Asr until the sun sets, there are many texts concerning the excellence of this. Likewise there are many texts concerning the remberances to be said in the morning and evening and concerning the excellence of one who remembers Allah when awaking and when sleeping.
The Salaf would place greater emphasis on the end of the day than the beginning. Ibn al-Mubarak said, ‘It has reached us that one who remembers Allah at the end of the day will be recorded as having performed remembrance throughout the day.’ Abu Jald said, ‘It has reached us that Allah, Exalted is He, descends to the lowest heaven during the eve of every day and looks at the deeds of the children of Adam.’
A hadith mentions, “Remembrance after Fajr is more beloved than freeing for slaves and remembrance after Asr is better than freeing eight slaves.” (Ahmad)
The end of the day of Jumu’ah is better than its beginning due to its containing an hour wherein the supplication is answered. (Bukhari) The end of the Day of Arafat is better than the beginning because the end of the day is the time for standing. The end of the night is better than the beginning of the night as was stated by the Salaf and they adduced the hadith to the Descent as proof. (Bukhari)
All of these facts strengthen the opinion of those who say that Asr is the “Middle Prayer”.
The Journey to Allah by Ibn Rajab Al-Hanbali Pages 52-57