Abu Hurayrah (radhiyallahu anhu) reported that Rasooulllah (Sallallahu alayhi wa sallam) said: “Whoever is treated with cupping on the seventeenth, nineteenth or twenty first, will be healed from all diseases.” (Abu Dawood, 3861, and al-Bayhaqi, 9/340. The isnad is hasan).
Al Haafiz ibn Hajar (rahimahullah) said: “According to the doctors, the most efficacious cupping is that which is done at the second or third hour and neither on a full nor empty stomach. With regard to specific days for administering cupping, it was reported in a hadeeth narrated from Ibn ‘Umar (radhiyallahu anhu) by Ibn Maajah that Rasoolullah (Sallaallahu Alayhi wa Sallam) said: ‘Administer cupping, may Allah bless you, on Thursdays, and administer cupping on Mondays and Tuesdays, but avoid cupping on Wednesdays, Fridays, Saturdays and Sundays.’ It was reported with two da’eef isnads, and there is a third version, also da’eef, reported by al-Daaraqutni in al Afraad.
He also reported it with a jayyid isnaad from Ibn ‘Umar but it is mawqoof (the isnad stops at the Sahaabi). Al Khallaal reported that Ahmad disliked cupping on the days mentioned, even though the hadeeth was not proven. It was said that a man was treated with cupping on a Wednesday and he developed leprosy because he ignored the hadeeth.
Abu Dawood (rahimahullah) reported from Abu Bakrah that he disliked cupping on Tuesdays, and said: “The Messenger of Allah (Sallallhu Alayhi wa Sallam) said: ‘Tuesday is the day of blood, and on that day there is an hour when blood does not stop.’ The doctors are agreed that cupping in the second half of the month, especially in the third quarter, is more beneficial than cupping at the beginning or end of the month.
Al-Muwaffaq al Baghdaadi said: The body fluids (humours) flow heavily at the beginning of the month and calm down at the end, so the best time to let the blood flow is in the middle of the month.” (Fath al Baari by Ibn Hajar, 10/149)
Imaam Ibn al Qayyim (rahimahullah) said:
“These ahaadeeth coincide with what the doctors agree on, that cupping should be done in the second half of the month, and that the third quarter of the month is better than the beginning or the end. But if cupping is done out of necessity it is beneficial at any time, even at the beginning or end of the month. Al Khallaal said: ‘Ismah ibn ‘Isaam told me: Hanbal told me: Abu ‘Abdullah Ahmad ibn Hanbal would be treated with cupping whenever his blood increased, no matter what time it was. They disliked having cupping done on a full stomach, because that could lead to obstruction and grievous diseases, especially if the food was heavy and bad. Choosing the times mentioned above for cupping is an extra precaution, to be on the safe side and to protect one’s health, but when it comes to treating disease, whenever it is necessary it should be used”. (al Ma’aad by Ibn al-Qayyim, 4/60)
Shaykh Munajjad mentions “It is clear from the above that the ahaadeeth which specify a particular time, when taken as a whole, indicate that there is a basis for this, especially since the words of the doctors are in agreement with it. If the seventeenth or nineteenth or twenty-first of a hijri month happens to be a Thursday, this is the best possible time for cupping, but this is not to say that it is not good to do it at other times. As a form of medical treatment, cupping should not be restricted to any particular time; it should be done as needed by the patient.
Some Muhadditheen explain that on the above days the full moon has a gravitational impact on many things on earth. For example, the sea has high tides due to the full moon. Similarly, the flowing of the blood is also affected and flows faster during the full moon. And Allah knows best.