Hadith: The Prophet (may Allah's peace and blessings be upon him) delayed the ‘Ishā' prayer until part of the night had passed and it was dark. ‘Umar came to him saying: O Messenger of Allah, come to pray, the women and children have slept. He came out with his head dripping with water and said: Had it not been hard for my Ummah, I would have commanded them to perform that prayer at this hour

عن عَبْد اللَّهِ بْنِ عَبَّاسٍ رضي الله عنهما قال: «أّعْتَمَ النَبِيُّ -صلَّى الله عليه وسلَّم- بِالعِشَاء، فَخَرَج عُمَر فقال: الصَّلاةَ يا رسول الله، رَقَد النِسَاءُ والصِّبيَان. فَخَرَجَ ورَأسُهُ يَقطُر يقول: لَولاَ أن أَشُقَّ عَلَى أُمَّتِي -أو على النَّاس- لَأَمَرتُهُم بهذه الصَّلاة هذه السَّاعَة».
[صحيح] - [متفق عليه]

‘Abdullāh ibn ‘Abbās (may Allah be pleased with him) reported: The Prophet (may Allah's peace and blessings be upon him) delayed the ‘Ishā' prayer until part of the night had passed and it was dark. ‘Umar came to him saying: "O Messenger of Allah, come to pray, the women and children have slept." He came out with his head dripping with water and said: "Had it not been hard for my Ummah, I would have commanded them to perform that prayer at this hour."
[Authentic hadith] - [Narrated by Bukhari & Muslim]

Explanation

The Prophet (may Allah's peace and blessings be upon him) delayed the ‘Ishā' prayer until part of the night had passed and the women and children, who are likely unable to stay late at night, had gone to sleep. ‘Umar ibn al-Khattāb (may Allah be pleased with him) came to him and said: “Come to pray, for the women and children have slept.” The Prophet (may Allah's peace and blessings be upon him) came out of his home and went to the mosque while his head was dripping with water from the ritual bath and he said: "Had it not been hard for my Ummah, I would have commanded them to perform that prayer at this hour." This indicates that it would have been better to delay ‘Ishā' prayer were it not for the hardship that would result from waiting for such a long time.