Musannaf Ibn Abi Shayba 3:5302

Hussain bin Ali narrated to us, from Za’idah, from Hisham, from Al-Hasan, who said: Whoever leads the people in prayer during Ramadan should adopt ease for them. If he is slow in recitation, let him complete one recitation of the Quran. If his recitation is between that, then one and a half recitations. If he is fast in recitation, then two recitations.