A Christian woman is asking about cupping
Question

In your numerous pages of disallowed matters you state that cupping is forbidden on certain days and allowed on others. I am not muslin but I am studying this religion and wanted to know exactly what cupping is.
Praise be to Allah.The rulings of Islam were revealed from Allaah, and Allaah has decreed that this religion is the final religion, and that our Prophet Muhammad (peace and blessings of Allaah be upon him) is the last of the Prophets. Allaah sent him to all of mankind and made the Qur’aan His miraculous Book until the Day of Resurrection. The Sunnah of the Prophet (peace and blessings of Allaah be upon him) is also revelation from Allaah. 
It is no wonder that the Prophet (peace and blessings of Allaah be upon him) told us of things that were revealed to him from his Lord, and these include information about scientific matters that were unknown at that time. This is a miracle which serves as proof that he is a true Prophet. The Prophet (peace and blessings of Allaah be upon him) was not a doctor but he told of some things that have been confirmed by modern medicine to be true. The Prophet (peace and blessings of Allaah be upon him) did not have laboratories or x-rays, but he spoke of things which mankind did not know to be true until after they were tested in laboratories and seen under microscopes. 
There are many examples of that, but this is not the place to discuss it in detail. Here we will limit our comments to cupping. We have already spoken of cupping and some of its benefits in the answer to question no. 21406 . 
What is cupping?
Cupping means letting out bad blood that is beneath the skin. 
It is a kind of medical treatment: 
It was narrated from Ibn ‘Abbaas that the Prophet (peace and blessings of Allaah be upon him) said: “Healing is in three things: in the incision of the cupper, in drinking honey and in cauterizing with fire, but I forbid my ummah (nation) to use cauterization.”  
Narrated by al-Bukhaari, 5356. 
It was narrated that Jaabir ibn ‘Abd-Allaah (may Allaah be pleased with him) said: I heard the Prophet (peace and blessings of Allaah be upon him) say: “If there is anything good in your medical treatments, it is in the incision of the cupper, drinking honey or in touching with fire when there is certainty that this will cure the disease, but I do not like to be cauterized.” 
Narrated by al-Bukhaari, 5359; Muslim, 2205 
The angels advised the Prophet (peace and blessings of Allaah be upon him) and his ummah to use cupping. 
The Messenger of Allaah (peace and blessings of Allaah be upon him) said: “I did not pass by any group of angels on the night of the Isra’ [the Prophet’s night journey when he was taken from Makkah to Jerusalem and back in the course of a single night], but all of them said to me, “You should use cupping, O Muhammad.” 
Classed as saheeh by Shaykh al-Albaani in al-Silsilah al-Saheehah, 2263. 
Our Prophet (peace and blessings of Allaah be upon him) was treated by means of cupping: 
It was narrated from Ibn ‘Abbaas (may Allaah be pleased with him) that the Prophet (peace and blessings of Allaah be upon him) was treated with cupping when he was in ihraam [a special state of devotion at the time of pilgrimage to Makkah], and he was treated with cupping when he was fasting. 
Narrated by al-Bukhaari, 1836. 
Some of his companions stated that he was treated with cupping for a pain in the head, i.e. a “migraine”. 
It was narrated from Ibn ‘Abbaas that the Prophet (peace and blessings of Allaah be upon him) was treated with cupping in his head for pain when he was in ihraam, at an oasis called Lahi Jamal.  
And it was narrated from him that the Messenger of Allaah (peace and blessings of Allaah be upon him) was treated with cupping on his head when he was in ihraam for a migraine that he was suffering. 
Narrated by al-Bukhaari, 5374. 
It was narrated from Ibn Buhaynah that the Prophet (peace and blessings of Allaah be upon him) was treated with cupping on the way to Makkah when he was in ihraam, in the middle of his head. 
Narrated by al-Bukhaari, 1739; Muslim, 1203. 
Lahi Jamal is a place on the way to Makkah. 
His companions were treated with cupping and they recommended it: 
Muslim (2205) narrated that ‘Aasim ibn ‘Umar ibn Qataadah said:  
Jaabir ibn ‘Abd-Allaah came to us and there was a man suffering from an abscess or a wound. He said, “What is wrong with you?” He said, “An abscess that is causing me pain.” He said, “O boy, bring me a cupper.” He said, “What will you do with a cupper, O Abu ‘Abd-Allaah?” He said, “I want to apply a cupping glass to him.” He said, “By Allaah, even if the flies land on me it hurts me, or if my garment touches me it hurts me.” When he saw how reluctant he was, he said, “I heard the Messenger of Allaah (peace and blessings of Allaah be upon him) say, ‘If there is anything good in your medical treatments, it is in the incision of the cupper, drinking honey or in touching with fire.’ And the Messenger of Allaah (peace and blessings of Allaah be upon him) said: ‘But I would not like to be cauterized.’” Then he brought the cupper and made the incision, and his problem went away. 
Recommendation of cupping on certain days of the month
It was narrated that Ibn ‘Abbaas (may Allaah be pleased with him) said: The Messenger of Allaah (peace and blessings of Allaah be upon him) said:  “The best days for cupping are the seventeenth, nineteenth and twenty first [of the months of the Islamic Hijri calendar]. I did not pass by any group of angels on the night of the Isra’ [the Prophet’s night journey when he was taken from Makkah to Jerusalem and back in the course of a single night], but all of them said to me, “You should use cupping, O Muhammad.” 
Narrated by Ahmad, 3306. Classed as saheeh by al-Albaani in al-Silsilah al-Saheehah, 1847. 
Recommendation to avoid cupping on certain days of the week 
What the questioner has read on our site appears in the book, “Things which are forbidden according to sharee’ah.” 
It was narrated that Ibn ‘Umar said: The Messenger of Allaah (S) said: “Cupping on an empty stomach is better, and there is healing and barakah (blessing) in it. It improves clarity of mind and the memory. So use cupping with the blessing of Allaah on Thursdays, and avoid cupping on Wednesdays, Fridays, Saturdays and Sundays, and use cupping on Mondays and Tuesdays, for that is the day when Allaah relieved Ayyoob (Job) of his afflictions, and He smote him with those afflictions on a Wednesday. So no leprosy begins except on a Wednesday or the night of Wednesday.” 
Narrated by Ibn Maajah, 3487. Classed as saheeh by al-Albaani in al-Silsilah al-Saheehah, 766. 
Cupping in modern medicine
Modern medicine has proven that cupping brings many benefits, and numerous books have been written about that, such as al-Dawa’ al-‘Ajeeb alladi shafa min Marad al-Qalb al-Qaatil wa’l-Shalal wa’l-Shaqeeqah wa’l-‘Uqum wa’l-Sarataan wa Marad al-Naa’oor al-Waraathi al-Haemophilia (The Amazing Cure that may heal fatal heart disease, paralysis, migraine, infertility, cancer and the genetic disease haemophilia). This is the most recent and most important book that has been published recently by the researcher ‘Abd al-Qaadir Yahya, which deals with the science of cupping. 
This book is regarded as a scientific reference and medical dictionary that is unique in the world because of its excellent explanations and scientific evidence. It is divided into 12 chapters, covering 500 pages. 
In the last chapter, he quotes clinical reports on the condition of some patients who recovered or whose condition improved with the application of cupping, by comparing the reports on their sickness before cupping and after cupping was applied. He also quotes the testimony of opinions of members of the Syrian medical team who took part in the research on cupping, who numbered 25 clinical and laboratory experts. 
Details of the physical benefits of cupping
1 – Modern science has proven that cupping may be a cure for some heart diseases, some blood diseases and some liver diseases. In cases where the lungs have become swollen because of heart failure, when all means of treatment such as use of diuretics, tying the hands and feet to reduce the flow of blood to the heart have failed, releasing some of the blood by opening a vein may be essential, to bring about a rapid recovery from heart failure. Similarly in the event of a sudden rise in blood pressure accompanied by semi-consciousness and a loss of awareness of time and place, or accompanied by unconsciousness as a result of the sudden increase in blood pressure, releasing some of the blood by opening a vein may be a treatment for such cases. Similarly, for some liver diseases such as cirrhosis there may be no effective remedy apart from releasing some of the blood by opening a vein. There are also some blood diseases which are distinguished by overproduction of red blood cells and a high ratio of haemoglobin in the blood, which require releasing some of the blood by opening a vein, which is the most effective treatment in such cases, so as to avoid further complications. It is worth mentioning that an increase in red blood cells may be the result of living in the mountains at high altitude and a low ratio of oxygen in the air, or it may be the result of intense heat that has an obvious effect of increasing glandular excretions, which leads to an increase in the number of red blood cells. So releasing some of the blood by opening a vein is the appropriate treatment in such cases. Hence the Prophet (peace and blessings of Allaah be upon him) said: “The best of the remedies that you use is cupping.” Narrated by Ahmad, 11634; classed as saheeh by al-Albaani in al-Silsilah al-Saheehah, 1053. This is a view which is approved by science, as has recently been confirmed by scientific research. 
Ref: al-‘I’jaaz al-‘Ilmi fi’l-Islam wa’l-Sunnah al-Nabawiyyah, by Muhammad Kaamil ‘Abd al-Samad. 
It should be noted that the author used the word fasd (opening a vein, venesection) instead of hijaamah (cupping). It is well known that there is a difference between the two. Fasd (opening a vein) means taking blood from the veins, which is more like having a blood sample taken, and cupping means removing bad blood from beneath the skin. 
2 – Ibn al-Qayyim al-Jawziyyah – who was well-versed in medicine – said: 
Cupping on the upper back helps to relieve pain in the shoulder and throat. Cupping on the veins on the side of the neck is beneficial in relieving  diseases of the head and its parts such as the face, teeth, ears and eyes (and the nose and throat if applicable) which are caused by an excess of blood or corruption thereof, or by both. 
Zaad al-Ma’aad, 4/55, 56 
Al-Tirmidhi (2051) narrated that Anas said: The Messenger of Allaah (S) used to have cupping done on the veins on the side of the neck and the upper back. 
We ask Allaah to make this answer beneficial for you, and we ask Allaah to open your heart to the truth and make it easy for you to do that which He loves and is pleased with. 
And Allaah knows best.