1. Ali ibn Muhammad has narrated from Sahl ibn Ziyad from Ali ibn Mahziyar from who has said the following:

“Abu al-Hassan ibn al-Husayn once wrote to Abu Ja‘far, al-Thaniy , ‘With me, I pray to Allah to keep my soul in service for your cause, people of your followers disagree on timing of dawn Salah (prayer). Certain ones of them perform when it is the first dawn in which a rectangular line appears in the sky, and others among them perform the morning Salah (prayer) when it (brightness) is at the bottom of the horizon and it has just appeared. I do not know which one is better, so I perform my Salah (prayer) in that time. If you consider it proper, instruct me about the time, which is better. Define it for me and how I should deal with the moon and the dawn with which it is not distinguishable, until it becomes red and it is dawn; and how should I deal with clouds and what are the limits for it during a journey or when one is at home. I will follow your instructions. 5 He (the Imam) wrote back with his own handwriting and I read it: “Dawn, Allah has granted you kindness, is when the white line appears sideways; and it is not vertical, during which time you do not perform Salah (prayer) on a journey or when at home until it is obvious. Allah, most Blessed, most High, does not leave His creatures in confusion in this matter so He has said, ‘Eat and drink until a white line appears from a darkness line at dawn. 5 (2:187) The white line is that which is sideways and after the appearance of which eating and drinking become unlawful because of fasting, and so also Salah (prayer) becomes obligatory at such time.’”