(a) It is narrated from Sayyiduna Abdullah bin Amr bin al-As (may Allah be pleased with them both) that the Messenger of Allah (peace and blessings be upon him) said: "The time of the Isha prayer is up to half of the night."
(b) It is narrated from Qatadah (may Allah have mercy on him): up to the middle half of the night.
(c) And in the hadith of Hisham, it is reported from Qatadah (may Allah have mercy on him): "When you pray Isha, its time is up to half of the night."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 1753