All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
The scholars stated a number of times when sleeping is disliked, among which is the period after the Fajr prayer as this is a time of blessings, hard work, activity and striving to earn one’s livelihood. Sakhar Al-Ghaamidi narrated that the Prophet said: "O Allaah! Bless my nation in its early times." Moreover, if he had to dispatch a battalion or an army, he would send it at the beginning of the day." (i.e. after Fajr) [Ahmad, Abu Daawood, At-Tirmithi, An-Nasaa’i and Ibn Maajah]
Ibn Al-Qayyim said,
“The morning sleep prevents (people from gaining) sustenance as this is a time when the creation looks for provision. It is also the time when the sustenance is being divided. Thus, if a person sleeps at this time, he prevents himself (from sustenance) except in case of an obstacle or a necessity. Besides, morning sleep is very harmful for the body as it makes it lazy and exhausts the secretions that should be transformed by sport (physical exercise), so morning sleep causes breaking up, tiredness and weakness. If this happens before defecating, physical activity and sport or occupying the stomach with something, then this is an incurable disease that causes many kinds of diseases.”
It is also reported that Ibn ‘Abbaas saw one of his sons asleep in the morning and he said to him, ‘Get up you! Are you going to sleep at a time when the sustenance is being distributed?” Besides, it was reported from some Taabi’is (the generation that followed the generation of the Companions) that the earth complains about the sleep of a scholar after the Fajr prayer.
Among the other times when sleeping is disliked is the time after the ‘Asr prayer, as some scholars from the Salaf (righteous predecessors) disliked sleeping after ‘Asr. Ibn Abu Shaybah narrated from Makhool that he used to dislike sleeping after ‘Asr and he said, “It is feared that the doer [the person who sleeps after ‘Asr] may be afflicted by whispers.”
Moreover, some scholars from the Salaf said, “If a person sleeps after ‘Asr and he loses his mind, then he should only blame himself.” It might be that they concluded this from experience and medicine as they did not provide evidence for this from a verse of the Book of Allaah or a Hadeeth from the Prophet .
Sleeping is also disliked in the time after Maghrib as it is confirmed that the Prophet disliked sleeping before 'Ishaa' and socializing and discussing (needlessly) after it, and the reason that it is disliked is that sleeping before it may lead to abandoning the prayer until its prescribed fixed time is over.
For more benefit, please refer to Fatwa 88494.
Allaah Knows best.