We do not know of any particular Du`a' to be said by Muslims in Salat-ul-`Eid or the day of `Eid (Festival). However, it is recommended for them to recite Takbir (saying: "Allahu Akbar [Allah is the Greatest]"), Tasbih (saying: "Subhan Allah [Glory be to Allah]"), Tahlil (saying: "La ilaha illa Allah [There is no god except Allah]"), and Tahmid (saying: "Al-hamdu lillah [All praise is due to Allah]") during the two nights before `Eid-ul-Fitr (the Festival of Breaking the Fast) and `Eid-ul-Adha (the Festival of the Sacrifice), the day of `Eid-ul-Fitr until the Khutbah (sermon) finishes, the days of `Eid-ul-Adha until the end of Days of Tashriq (11th, 12th and 13th of Dhul-Hijjah), and the first ten days of Dhul-Hijjah for Allah (Glorified be He) says regarding `Eid-ul-Fitr:
(He wants that you) must complete the same number (of days), and that you must magnify Allâh [i.e. to say Takbîr (Allâhu Akbar; Allâh is the Most Great)] for having guided you
(Part No. 8; Page No. 303) There are also some Hadiths and Athar (narrations from the Companions) to the same effect.May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.