Al-Husayn ibn Said, from Fadalah, from Hammad, from Zayd al-Shahham, who said:
I heard Abu Abdillah عليه السلام, peace be upon him, saying, “A man shortens (the prayer) at the journey of twelve miles (four farsakhs).”
Ali Akbar al-Ghaffari
Tahdhīb al-Aḥkām fī Sharḥ al-Muqniʿah, vol. 4, p. 291