Ahmad ibn Muhammad ibn Isa, from Ali ibn Hakam, from Abdullah ibn Yahya al-Kahili, who said: I (narrator) heard Abu Abdillah عليه السلام, saying regarding shortening the prayer. Imam عليه السلام said: “A barid by a barid is twenty-four miles.” Then Imam عليه السلام said: “Indeed, my father عليه السلام used to say, ‘Shortening was not set according to the swift mule (al-baghlah al-safwa) or the fast mount (al-dabbah al-najiyah), but rather it was set according to the travelling pace of the caravan (al-qitar).’”