Sahih Muslim
The Book of Prayers (Kitab Al-Salat)
Book Number: 004 / Hadith Number: 1351
Sayyar b. Salama reported: I heard Abu Barza saying that the Messenger of Allah (may peace be upon him) did not mind some delay in the 'Isya' prayer even up to the midnight and he did not like sleeping before (observing it) and talking after it. Shu'ba said: I again met him (Sayyar b. Salama) for the second time and he said: Even up to the third (part) of the night.