Sahih Muslim Book 4, Hadith Number 1379.

Chapter : Forbiddance to go out of the mosque after the Adhan has been announced by the Mu’adhdhin.

‘Abd al-Rahman b. Abd ‘Amr reported: ‘Uthman b. ‘Affan (narrated the mosque after evening prayer and sat alone. I also sat alone with him, so he said: O, son of m brother, I heard tile Messenger of Allah (may peace be upon him) say: He who observed the ‘Isha prayer in congregation, it was as if he prayed up to the midnight, and he who prayed the morning prayer in congregation, it was as if he prayed the whole night.