Ubaydullah bin Abdullah bin Utbah (may Allah have mercy on him) says: It is the Sunnah for the imam to say takbir on the pulpit before the sermon on the day of Eid al-Fitr and Eid al-Adha. Before the sermon, standing on the pulpit, the imam should say nine takbirs in succession without separating them with speech; then he should deliver the sermon, then sit for a short while, then stand for the second sermon, then say seven takbirs in succession, without separating them with speech; then deliver the sermon.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب صلاة العيدين / 6217