Narrated by Muhammad ibn Ya’qub from Muhammad ibn Yahya from Ahmad ibn Muhammad from Abdullah ibn Muhammad al-Hajjal from Tha’labah ibn Maymun from ‘Imran ibn Ali al-Halabi. He said: I asked Abu Abdillah عليه السلام: "When does the ‘Atamah (‘Ishaʾ prayer) become obligatory?" Imam عليه السلام said: "When the shafaq disappears, and shafaq is the redness (in the sky)." ‘Ubaydullah asked: "May Allah سبحانه وتعالى set you right, indeed after the redness disappears, there remains a strong light spread across (the horizon)." Abu Abdillah عليه السلام said: "Indeed, the shafaq is only the redness, and the light is not from the shafaq."