In terms of the best days of the week, the Messenger (peace be upon him) said, ‘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 this is the day that Ayoob was befallen with a trial. You will not find leprosy except (by being cupped) on Wednesday or Wednesday night.’ (Ibn Maajah).
From the previous two narrations, we deduce that the best days for cupping are the 17th, 19th and 21st of the lunar month, which coincide with Monday, Tuesday or Thursday. However, when one is sick or is in dire need then cupping can be performed on any day.