Allah says here:

(Did they not disbelieve in that which was given to Musa of old) Did not mankind disbelieve in those mighty signs which were given to Musa

(They say: "Two kinds of magic, each helping the other!'') cooperating or working one with the other.

(And they say: "Verily, in both we are disbelievers.'') meaning, `we disbelieve in each of them.' Because of the close relationship between Musa and Harun, mention of one includes the other.