Ruling on the najaasah (impurity) of pork

I read: Plates, spoons and knifes that have been in contact with pork must be washed 7 times with water and 1 time with sand. Is that right or not?Witch hadith this rule is based on? Is it not sufficient to wash the plates one time with soup?

Praise be to Allaah.

Pork is haraam and it is not permissible to eat it, whether it is the meat, fat or any other part, because Allaah says (interpretation of the meaning): 

“Forbidden to you (for food) are: Al-Maitah (the dead animals — cattle — beast not slaughtered), blood, the flesh of swine[al-Maa’idah 5:3] 

The Muslims are agreed that all parts of the pig are haraam. Allaah has forbidden it because of the harmful things it contains and because it is impure, as Allaah says (interpretation of the meaning): 

“Say (O Muhammad): ‘I find not in that which has been revealed to me anything forbidden to be eaten by one who wishes to eat it, unless it be Maitah (a dead animal) or blood poured forth (by slaughtering or the like), or the flesh of swine (pork); for that surely, is impure…”[al-An’aam 6:145] 

Its meat is a disease, and the more people advance in knowledge, the more new diseases they discover, because of pork consumption.  

Muslims should keep away from places where this filthy meat is eaten so that they will not eat anything of it without realizing. 

With regard to washing plates, it is sufficient to wash them well with whatever will get rid of the filth of this meat. 

Because the correct view is that the impurity caused by pork is like any other impurity; there is no need to wash it seven times, one of which should be with earth.
See al-Sharh al-Mumti’ by Ibn ‘Uthaymeen, 1/356. And Allaah knows best.