'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: 0, son of my brother, I heard the Messenger of Allah (ﷺ) say: He who observed the 'Isha' prayer in congregation, it was as if he prayed up to midnight, and he who prayed the morning prayer in congregation, it was as if he prayed the whole night.
Source: sunnah.com
Other translations
Arabic
حَدَّثَنَا إِسْحَاقُ بْنُ إِبْرَاهِيمَ، أَخْبَرَنَا الْمُغِيرَةُ بْنُ سَلَمَةَ الْمَخْزُومِيُّ، حَدَّثَنَا عَبْدُ الْوَاحِدِ، - وَهُوَ ابْنُ زِيَادٍ - حَدَّثَنَا عُثْمَانُ بْنُ حَكِيمٍ، حَدَّثَنَا عَبْدُ الرَّحْمَنِ بْنُ أَبِي عَمْرَةَ، قَالَ دَخَلَ عُثْمَانُ بْنُ عَفَّانَ الْمَسْجِدَ بَعْدَ صَلاَةِ الْمَغْرِبِ فَقَعَدَ وَحْدَهُ فَقَعَدْتُ إِلَيْهِ فَقَالَ يَا ابْنَ أَخِي سَمِعْتُ رَسُولَ اللَّهِ صلى الله عليه وسلم يَقُولُ " مَنْ صَلَّى الْعِشَاءَ فِي جَمَاعَةٍ فَكَأَنَّمَا قَامَ نِصْفَ اللَّيْلِ وَمَنْ صَلَّى الصُّبْحَ فِي جَمَاعَةٍ فَكَأَنَّمَا صَلَّى اللَّيْلَ كُلَّهُ " .
sunnah.com