Muhammad ibn Ya‘qub from Ali ibn Ibrahim from his father from Hammad from Hariz from Zurarah who said:
Abu Ja‘far عليه السلام, peace be upon him, said: “The Adhan is to be pronounced clearly, with articulation of the Alif’ and the ‘ha’, and the Iqamah is to be recited quickly in a flowing manner.”
Ali Akbar al-Ghaffari
Tahdhīb al-Aḥkām fī Sharḥ al-Muqniʿah, vol. 2, p. 63