Is it necessary to wash the clothes and vessels of one who enters Islam?

That is not necessary, because the more correct view is that the najaasah of non-Muslims is intangible, not tangible, because the Prophet (peace and blessings of Allaah be upon him) and his companions did wudoo’ after drinking from the leather vessel of a mushrik woman, and because Allaah has permitted us to marry the women of the People of the Book (i.e., Jewish and Christian women), which implies touching them. And because Allaah has permitted the food of those to whom the Book was given, which also usually implies that they must have touched the food. 

Based on that, if a man becomes Muslim he does not have to wash his clothes, bedding and so on, unless he is certain that some najaasah (impurity) got onto them and they have not been purified from it. End quote. 

Shaykh Ibn ‘Uthaymeen (may Allaah have mercy on him).