Riyad as-Salihin 1071
'Uthman bin 'Affan (May Allah be pleased with him) reported:
I heard the Messenger of Allah (ﷺ) saying: "One who performs 'Isha' prayer in congregation, is as if he has performed Salat for half of the night. And one who performs the Fajr prayer in congregation, is as if he has performed Salat the whole night." [Muslim] The narration of At-Tirmidhi says: 'Uthman bin Affan (May Allah be pleased with him) narrated that he had heard the Messenger of Allah (ﷺ) saying: "He who attends 'Isha' in congregation, is as if he has performed Salat for half of the night; and he who attends 'Isha' and Fajr prayers in congregation, is as if he has performed Salat for the whole night."
عن عثمان بن عفان رضي الله عنه قال‏:‏ سمعت رسول الله صلى الله عليه وسلم يقول‏:‏ ‏"‏من صلى العشاء في جماعة، فكأنما قام نصف الليل ومن صلى الصبح في جماعة، فكانما صلى الليل كله‏"‏ ‏(‏‏(‏رواه مسلم‏)‏‏)‏‏.‏ 
وفي رواية الترمذي عن عثمان بن عفان رضي الله عنه قال‏:‏ قال رسول الله صلى الله عليه وسلم ‏:‏ ‏"‏من شهد العشاء في جماعة كان له قيام نصف ليلة، ومن شهد العشاء والفجر في جماعة، كان له كقيام ليلة‏"‏ ‏(‏‏(‏قال الترمذي حديث حسن صحيح‏)‏‏)‏