Al-Husayn ibn Said, from Fadalah, from Muawiyah ibn Wahb, who said:
I (narrator) said: “What is the least distance in which the traveller shortens the prayer?” He said: “One barid going and one barid coming.”
Ali Akbar al-Ghaffari
Tahdhīb al-Aḥkām fī Sharḥ al-Muqniʿah, vol. 4, p. 291