What are the Days of Husōm, when do they occur, and what is the extent of validity of the common belief regarding the disapproval of marriage during them?

The days of Al-Hassum were a torment upon the people of 'Aad, not days of ill omen that prevent marriage. Ibn Kathir said in his interpretation of "a day of misfortune" (yawm nahs): meaning its misfortune and destruction were continuous upon them. As for what is mentioned about the last Wednesday of the month being a continuous day of misfortune, some scholars have rejected it. Al-Suhaili mentioned that the misfortune of Wednesday only affects those who are pessimistic and superstitious. As for those who trust in Allah, it will not harm them. It is possible that the warning against Wednesday is due to the punishment that descended on that day. Scholars have stated that the Hadith "The last Wednesday of the month is a continuous day of misfortune" is not authentic.