Imam Bukhari narrates: Sulaiman bin Harb narrated to us, he said: Hammad bin Zaid narrated to us from Simak bin Atiyyah from Ayyub from Abi Qilabah from Anas, may Allāh be pleased with him, he said that

Bilal, may Allāh be pleased with him, was commanded that he say the words of the Adhan twice each, and say the words of the Iqamah once each, except "Qad qamat is-salah."