Anas ibn Maalik (RA) reported that the Rasul (SAW) said, “Whoever wants to perform Hijama then let him search for the 17th, 19th and 21st…” Saheeh Sunan ibn Maajah (3486)].
These are the generally accepted dates to- H jama, irrespective of what day of the week they fall on, though there are other Ahadeeth that seem to prohibit having it done on particular days of the week, these Hadeeth are categorized as Daeef however and as such the days mentioned in them are not strictly prohibited, they are mentioned here for completeness:
Ibn Umar (RA) reported that the Rasul (SAW) said, “Hijama on an empty stomach is best. In it is a cure and a blessing. It improves the intellect and the memory. So cup yourselves with the b essing of Allaah on Thursday. Keep away from Hijama on Wednesday, Friday, Saturday and Sunday to be safe. Perform Hijama on Monday and Tuesday for it is the day that Allaah saved Ayoub from a thai. He was inflicted with the trial on Wednesday. You will not find leprosy except (by being cupped) on Wednesday or Wednesday night.” [Sunan ibn Maajah (3487).
Ibn Umar (RA) reported that the Rasul (SAW) said, “Hijama on an empty stomach is best. It increases the intellect and improves the memory. It improves the memory of the one memorising. So whoever is going to be cupped then (let it be) on a Thursday in the name of Allaah. Keep away from being cupped on a Friday, Saturday and Sunday. Be cupped on a Monday or Tuesday. Do not be cupped on a Wednesday because it is the day that Ayoub was befallen with a trial. You will not find leprosy except (by being cupped) on Wednesday or Wednesday night.” [Sunan ibn Maajah 3488].
In reconciling these it can be said that for Hijama in strength, the dates are specified, they are the 17th, 19th or 21st of the lunar month and the best is when these dates coincide with a Monday, Tuesday or Thursday, though there is no prohibition for having this type of Hijama done on any other day as long as it corresponds with the 17th, 19th and 21st.
(There is difference of opinion regarding the prohibition on particular days of the week, since another way of reconciling is considering that the Nabi of Allaah (SAW) in the above two Ahadeeth was referring to that particular month in which the Hadeeth was narrated and referring directly to the days of that week and the week after. If Thursday was the 19th, then the previous Friday, Saturday and Sunday would be the 13th, 14th and 15th, and on these days of the Islaamic month it is mentioned that cupping should not be done, Monday and Tuesday would be the 16th and 17th which would be okay for cupping, since they are after the full moon. Wednesday being prohibited in this case would be the exact day of the year that corresponded with the illness of Nabi Ayyoob (AS), and Thursday being the ideal day to perform Hijama.
It is important to note that this type of Hijama (i.e. Hijama in strength /Sunnah Hijama) should be performed only in the seasons of spring andsummer. When the climate is hot. However, in places like Hejaz where it is hot throughout the year it can also be performed in the other Season.