Mujahid bin Jabr said, "The Jews told Quraysh to say this to Muhammad , then 
Allah said: `Did they not disbelieve in that which was given to Musa of old They 
say: Two kinds of magic, each helping the other!' This refers to Musa and Harun, 
may the peace and blessings of Allah be upon them both,
[تَظَـهَرَا]
(each helping the other) i.e., working together and supporting one another.'' 
This was also the view of Sa`id bin Jubayr and Abu Razin that the phrase "two 
kinds of magic'' referred to Musa and Harun. This is a good suggestion. And 
Allah knows best.