It was narrated from Ahmad ibn Ali ibn al-Hakam, from someone who narrated it from one of the two Imams, peace be upon them: He عليه السلام was asked about the time of Maghrib. Imam عليه السلام said: “When its ‘kursi’ disappears.” I asked: “What is its ‘kursi’?” Imam عليه السلام said: “Its disk (the sun’s disk).” I asked: “When does its disk disappear?” Imam عليه السلام said: “When you look at it and you no longer see it.”