It is narrated from Abdullah bin al-Harith al-Makhzumi that in the first (narration) he said that the time of Isha is when the redness disappears, and in the second he said that Abdullah bin al-Harith said: Then he said concerning Isha: "I think up to a third of the night."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 1747