Assalamualaikum Warahmatullahi Wabarakatuh

In the name of Allah, the Entirely Merciful, the Especially Merciful. O Allah! I seek refuge in You from knowingly associating partners with You in any way, and I seek Your forgiveness for that which I do not know. Ameen.
 

Sleeping is the best way to rest after being active all day. Sleeping is a passive activity that is very important for human's physical and mental health. With sufficient sleep, a person can restore stamina and be ready to carry out activities the next day.
 

In the Qur'an it is explained:

"And among the signs of His power are your sleep at night and during the day and your efforts to seek some of His bounties. Indeed, in these there are truly signs for a people who listen" (QS Ar-Rum  : 23)
 

However, there are certain times when it is not recommended to sleep.
 

Firstly, sleeping after the subuh until the sun rises. Sleeping during this time is considered as preventing people from getting the blessings of good fortune and life. This is Because these times are the times when the blessings of sustenance are given to someone.
 

Secondly, sleeping after 'Asr. Sleeping during this time is risky and it may reduce the active power of the perpetrator's mind. It explained from one of the hadith: 
 

"Whoever sleeps after Asr time and then loses his mind, then never blame him except himself" (HR Ad-Dailami).
 

Even though the scholars condemned the above hadith as a daif hadith (weak hadith), the above hadith is still relevant in the context of fadla'il al-a'mal (virtuous deeds).
 

Thirdly, sleeping before performing the 'Isha prayer. In one authentic hadith it is explained:
 

"Indeed, the Messenger of Allah did not like sleeping before the 'Isha prayer and talking after the 'Isha prayer" (HR al-Bukhari)
 

The reason why it is forbidden to sleep before performing the 'Isha prayer is due to fear that the 'Isha time will run out because of sleeping too soundly, as may become a habit of most people who sleep at night but without performing their 'Isha prayer.
 

Meanwhile, the sleeping time that is recommended by the syara' is sleeping during qailulah (a short rest) time. 
 

Some people interpret this qailulah time as sleeping before dhuhur time (the slipping of the sun), there are also those who interpret it after dhuhur time. What is certain is that the main function of qailulah sleep is as preparation for carrying out qiyam al-lail with prayer and dhikr at night.
 

As explained by Imam al-Ghazali:
 

"Sleeping qailulah is a sunnah that can help someone to carry out qiyam al-lail, just like sahur is a sunnah that functions to help someone fast during the day" (Al-Ghazali, Ihya' ulum ad-Din, juz 1, page 338  )
 

Apart from that, Sharia recommends us to make use their time to sleep and rest at night, whereas daytime is for work and activities. This pattern is considered ideal and in accordance with Islamic teachings.
 

This is as confirmed in the Qur'an:

"And We made the night a garment (sleeping time), and We made the day a means of earning a living" (QS An-Naba', verse: 10-11).

Wallahu'alam.