Muhammad b. al-Hasan b. Ahmad b. al-Walid narrated to us. He said: Muhammad b. al-Hasan al-Saffar narrated to us from al-`Abbas b. Ma`ruf from `Ali b. Mahzayar from al-Husayn b. Sa`id from `Ali b. al-Nu`man from Dawud b. Farqad. He said: I heard my father ask Aba `Abdillah al-Sadiq :

When does Maghrib time begin? So, he said: When its seat disappears. He said: What is its seat? He said: Its disk. He said: When does its disk disappear? He said: If you look to it, you do not see it.