Musnad Ahmad 25:1607

'Abd al-Razzaq and Ibn Bakr narrated to us, they said: Ibn Jurayj informed us, he said: I said to 'Ata': "Which time is most beloved to you for me to pray the 'Isha' prayer, whether as an Imam or alone?" He said: I heard Ibn 'Abbas say: The Messenger of Allah (ﷺ) delayed the 'Isha' prayer one night until the people slept and woke up, and slept and woke up. Then 'Umar ibn al-Khattab stood up and said: "The prayer." 'Ata' said: Ibn 'Abbas said: Then the Prophet of Allah (ﷺ) came out—it is as if I am looking at him now—his head was dripping with water, placing his hand on the side of his head. He said: "Were it not that it would be difficult for my Ummah, I would have commanded them to pray it like this."