Response: They should not be washed. Rather, if a person washes them with the intention of worshipping Allaah (by this action), then this is an innovation because the Prophet (sal-Allaahu `alayhe wa sallam) did not do this.
Shaykh Ibn 'Uthaymeen
al-Bid'u wal-Muhdathaat wa maa laa asla lahu - Page 404
Taken from fatwa-online.com