Musannaf Ibn Abi Shayba 13:2308

Abu Bakr narrated to us, he said: Waki’ narrated to us, he said: al-Mas’udi narrated to us, from al-Qasim, he said: There are four things for which no payment should be taken: the recitation of the Quran, the Adhan, the judiciary, and the distribution [of spoils or charity].