Al-Husayn ibn Sa‘id from Muhammad ibn Sinan from al-Hasan ibn al-Sarri:
Abu Abdillah عليه السلام said: “The Adhan is to be recited with measured recitation (‘tartil’), and the Iqamah is to be recited quickly in a flowing manner (‘hadr’).”
Ali Akbar al-Ghaffari
Tahdhīb al-Aḥkām fī Sharḥ al-Muqniʿah, vol. 2, p. 69