From Sahih Muslim (Hadith 2050):
Ata' reported that Ibn 'Abbas sent (him) to Ibn Zubair at the commencement of the oath of allegiance to him (for Caliphate saying):As there is no Adhan on 'Id-ul-Fitr, so you should not pronounce it. Ibn Zubair did not pronounce Adhan on that day. He (Ibn 'Abbas) also sent him (with this message) that sermon (is to be delivered) after the prayer, and thus it was done. So lbn Zubair observed prayer before Khutba
Reference: Muslim 2050