Al-Kāfi - Volume 3 > The Times of Maghrib and ‘Isha’ Salah (Prayer)
Hadith #4

4ـ عَلِيُّ بْنُ مُحَمَّدٍ عَنْ سَهْلِ بْنِ زِيَادٍ عَنْ مُحَمَّدِ بْنِ عِيسَى عَنِ ابْنِ أَبِي عُمَيْرٍ عَمَّنْ ذَكَرَهُ عَنْ أَبِي عَبْدِ الله (عَلَيْهِ الْسَّلام) قَالَ وَقْتُ سُقُوطِ الْقُرْصِ وَوُجُوبِ الإِفْطَارِ أَنْ تَقُومَ بِحِذَاءِ الْقِبْلَةِ وَتَتَفَقَّدَ الْحُمْرَةَ الَّتِي تَرْتَفِعُ مِنَ الْمَشْرِقِ فَإِذَا جَازَتْ قِمَّةَ الرَّأْسِ إِلَى نَاحِيَةِ الْمَغْرِبِ فَقَدْ وَجَبَ الإِفْطَارُ وَسَقَطَ الْقُرْصُ.

4. Ali ibn Muhammad has narrated from Sahl Ziyad from Muhammad ibn Isa from ibn abu ’Umayr from those whom he has mentioned who has said the following: "Abu ’Abd Allah has said, ‘The disappearance of the disk (the sun), the necessary time to discontinue fasting is when facing its direction and the disappearance of the redness that rise from the east upon its reaching overhead toward the west at such time fasting is discontinued; the (disappearance of the disk (sunset) has taken place.’”