What is the view of the Muslim Philosophers about azaab al-qabar (punishment of the grave)?

In a Nutshell:  Historically Muslim philosophers (from al-Kindi, al-Farabi to Ibn Sina and Ibn Rushd) didn't pay much attention to life in the grave. None discussed this issue. Their concerns related to attributes of the soul and its relationship with the body as well as their destiny. Al-Kindi Abu Yusuf al-Kindi (d. 256) was an Arab Muslim philosopher, polymath, mathematician, physician and musician. Al-Kindi does not tell us so much about the journey in the grave. He considered humans as having two parts: the body and the soul. The body is a dress for the soul, a slave under its authority. The human soul, after departing the body is considered as similar to God's essence. (Kamali, Muhadarat fi al-Falsafa al-Islamiyyah, p. 56; Muhammad Nassar, Fi al-Falsafa al-Islamiyyah, p. 68) Kindi comments: إن النفس عند أفلاطون وجلة الفلاسفة باقية بعد الموت وجوهرها كجوهر الباري في قوتها ... أو دون ذلك برتبة يسيرة ... وإذا تجردت وفارقت هذا البدن ... صارت في نور الباري ورأت الباري ... وصارت الأشياء بارزة لها كمثل ما هي بارزة للباري "The soul (nafs) according to Plato and all the philosophers continues (in existence) after death and its essence is similar to the essence of the Creator in its power … or slightly less than it … but when it leaves the body … it becomes within the light of the Creator and it will see the Creator … Everything is now visible to it as it is visible to the Creator." (Al-Kindi, Risalah Fi al-Qawl Fi an-Nafs, p. 63) In light of his understanding of the soul and its position after death, we could easily see why the grave is not mentioned in his philosophy; there is no room for it. The grave, according to al-Kindi, is nothing but the wastebasket of the worn-out body when the soul lives beside the Creator. (Rasa'il al-Kindi Fi al-Falsafa, Vol. 1, p. 277)   Al-Farabi Muhammad al-Farabi (d. 339 A.H.) was a Muslim philosopher and jurist. He also did not recognise the journey in the grave nor what happens to it. Like other philosophers, he only considers the soul believing the soul was created and continued after the death of the body and cannot be transmigrated to another body. He, however, believed in the happiness and the sadness of the soul after death. He says: ولا يجوز وجود النفس قبل البدن كما قال أفلاطون، ولا يجوز انتقال النفس من جسد إلى جسد كما يقول التناسخيون، وللنفس بعد البدن سعادات وشقاوات. "The existence of the soul before the body is not imaginable as Plato argued. The soul can't transmigrate from a body to another body as the Metempsychosis followers believe. The soul after leaving the body goes through happiness and miseries." (al-Farabi, 'Uyun al-Masa'il, p. 21) Whilst he believes in happiness and sadness after death, he considers them as some sort of spiritual and psychological notions. Most souls according to al-Farabi were ignorant and would perish; through which they would go through spiritual sadness. So there is no life after death (Hayat al-Barzakh) in the sense of material and real life, rather a spiritual eternity of happiness or a spiritual eternity of nihility. (al-Hilo, al-Wafi fi Tarikh al-Falsafa, p. 141) Ibn Sina (Avicenna) Ibn Sina (Avicenna, d. 427 A.H.) was a Persian polymath. He was a physician, astronomer, philosopher and writer in the Islamic Golden Age. His view of the soul and the grave is little different to the previous philosophers. He argued there were three kinds of souls: a perfect and infallible soul who would inherit eternal happiness, a perfect fallible soul who would inherit eternal happiness after a period of hardship, and an imperfect and fallible soul who would inherit eternal misery. Such happiness and sadness are exclusive for the souls as he saw the body as only a dress for the soul like the rest of the philosophers thus saying nothing in regard to the events in the grave. (Ibn Sina, al-Uddhwyah, p. 187) Ibn Rushd (Averroes) Ibn Rushd (Averroes, d. 595 A.H.) was a Muslim Spanish Andalusian philosopher. In relation to the punishment of the grave, he argued souls after death lives either a happy life due to their good deeds or a miserable life due to their sinful deeds. He even considered the belief of eternal life of the soul after death as one of the principles of faith ('usul al-Iman) and anyone who rejects it is was considered a disbeliever. إن كان من الأصول فالمتأول له كافر، مثل من يعتقد أنه لا سعادة أخروية هاهنا ولا شقاء. "If the matter is one of the principles (usul), anyone interprets (yata'awal) it otherwise is a disbeliever (kafir), such as the one who believes there is no happiness or sadness after death ('ukhrawi)." (Ibn Rushd, Fasl al-Maqal, p. 110) Like the above philosophers, he also said nothing about life in the grave. Conclusion Muslim philosophers, in general, don't pay much attention to life in the grave so all of them said nothing about this notion. They are more concerned with the attribute of the soul and its relationship with the body as well as their destiny. Al-Kindi believed in the relative equality between the essence of the Creator and the essence of the human soul, so the later resident beside Him after leaving the body. Al-Farabi and Ibn Sina believed in the spiritual happiness and misery for the souls depending on their deeds in the previous life. Ibn Rushd followed them, but he attributed some reality to such feelings. References al-'Itibi, al-Hayah al-Barzakhiyah. Kamali, Muhadarat fi al-Falsafa al-Islamyah. Muhammad Nassar, Fi al-Falsafa al-Islamiyah. Al-Kindi, Risalah Fi al-Qawl Fi an-Nafs. Rasa'il al-Kindi Fi al-Falsafa. al-Farabi, 'Uyun al-Masa'il. al-Hilo, al-Wafi Fi Tarikh al-Falsafa. Ibn Sina, al-Uddhwyah. Ibn Rushd, Fasl al-Maqal.