it is authentically reported that reciting the Takbir (saying: "Allahu Akbar [Allah is the Greatest]") on the Days of Tashriq (11th, 12th and 13th of Dhul-Hijjah) is Sunnah (an act following the example of the Prophet). Should the Imam (the one who leads congregational Prayer) recite the Takbir and then the people repeat it after him
or should each person recite the Takbir by themselves quietly or loudly?
Each person should recite the Takbir individually out loud. It has not been authentically reported from the Prophet (peace be upon him) that he performed a collective recitation of the Takbir, and he (peace be upon him) said,
“Anyone who does an action which is not in accordance with this matter of ours (Islam), will have it rejected.”
May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.