Sahih Bukhari Volume 001, Book 010, Hadith Number 545.
Narated By Ibn Juraij from Nafi : 'Abdullah bin 'Umar said, "Once Allah's Apostle was busy (at the time of the 'Isha'), so the prayer was delayed so much so that we slept and woke up and slept and woke up again. The Prophet came out and said, 'None amongst the dwellers of the earth but you have been waiting for the prayer." Ibn 'Umar did not find any harm in praying it earlier or in delaying it unless he was afraid that sleep might overwhelm him and he might miss the prayer, and sometimes he used to sleep before the 'Isha' prayer. Ibn Juraij said, "I said to 'Ata', 'I heard Ibn 'Abbas saying: Once Allah's Apostle delayed the 'Isha' prayer to such an extent that the people slept and got up and slept again and got up again. Then 'Umar bin Al-Khattab I, stood up and reminded the Prophet I of the prayer.' 'Ata' said, 'Ibn 'Abbas said: The Prophet came out as if I was looking at him at this time, and water was trickling from his head and he was putting his hand on his head and then said, 'Hadn't I thought it hard for my followers, I would have ordered them to pray ('Isha' prayer) at this time.' I asked 'Ata' for further information, how the Prophet had kept his hand on his head as he was told by Ibn 'Abbas. 'Ata' separated his fingers slightly and put their tips on the side of the head, brought the fingers downwards approximating them till the thumb touched the lobe of the ear at the side of the temple and the beard on the face. He neither slowed nor hurried in this action but he acted like that. The Prophet said: "Hadn't I thought it hard for my followers I would have ordered them to pray at this time."