It is narrated from Sayyiduna Ibn Abbas (may Allah be pleased with them both) that the Messenger of Allah (peace and blessings be upon him) delayed the ‘Isha prayer one night. It was said: “The prayer, O Messenger of Allah, the women and children have fallen asleep.” So you came out, and water was dripping from your side, and you (peace and blessings be upon you) said: “This is (the proper) time (for this prayer) if it were not difficult for my Ummah.”
Hadith Referenceسنن دارمي / من كتاب الصللاة / 1249
Hadith Gradingتحقیق (حسین سلیم أسد الدارانی):إسناده صحيح وابن جريج قد صرح بالتحديث عند مسلم، [مكتبه الشامله نمبر: 1251]
From all these narrations, it is established that delaying the ‘Isha prayer is more virtuous. However, may sacrifices be made for the Prophet of Mercy (sallallahu alayhi wa sallam), that out of consideration for the hardship upon the Ummah, he (sallallahu alayhi wa sallam) would often perform the ‘Isha prayer at its earliest time.
The time for the ‘Isha prayer is from the disappearance of the twilight (shafaq) until the first third of the night. Therefore, to delay the ‘Isha prayer until midnight or the end of the night is not correct; in such a case, it would be considered a missed (qada) prayer. However, it is more virtuous to perform the Witr and Tahajjud prayers before the break of dawn (tulu‘ al-subh).