«من صلى العشاء في جماعة كان كقيام نصف ليلة ومن صلى العشاء والفجر في جماعة كان كقيام ليلة»
The Prophet (peace and blessings be upon him) said:
"Whoever prays Isha in congregation, it is as if he stood in prayer for half the night; and whoever prays both Isha and Fajr in congregation, it is as if he stood in prayer for the whole night."
Hadith Referenceصحیح الجامع الصغیر / حرف الميم / 6342