Musannaf Ibn Abi Shayba 3:3323

Waki’ narrated to us, he said: Sufyan narrated to us, from Abu Ishaq, from al-Harith, from Ali, that he used to say the takbir during al-Fitr eleven times: six in the first [rak'ah] and five in the last. He would begin with the recitation in both rak'ahs. And [he used to say the takbir] five times during al-Adha: three in the first [rak'ah] and two in the last. He would begin with the recitation in both rak'ahs.