Muhammad ibn al-Hasan al-Saffar, from Muhammad ibn Isa, from Amr ibn Said, who said: Jafar ibn Ahmad wrote to him, asking him about ‘travel and at what distance shortening (of prayers) is required.’ So the Imam عليه السلام, peace be upon him, wrote in his own handwriting, and I recognized it. He said: “The Commander of the Faithful عليه السلام, peace be upon him, when he travelled and went out on a journey, would shorten at one farsakh.” Then in the following year, he repeated the question to him, so the Imam عليه السلام, peace be upon him, wrote to him: “In ten days.”