Sunan Ibn Majah, Hadith 200 ⓘ
It was narrated that Abu Sa'eed Al-Khudri said: "The Messenger of Allah said: 'Allah smiles at three things: a row in the prayer, a man who prays in the depths of the night, and a man who fights' I think he said, 'behind the battalion.'"
حَدَّثَنَا أَبُو كُرَيْبٍ، مُحَمَّدُ بْنُ الْعَلاَءِ حَدَّثَنَا عَبْدُ اللَّهِ بْنُ إِسْمَاعِيلَ، عَنْ مُجَالِدٍ، عَنْ أَبِي الْوَدَّاكِ، عَنْ أَبِي سَعِيدٍ الْخُدْرِيِّ، قَالَ قَالَ رَسُولُ اللَّهِ ـ صلى الله عليه وسلم ـ " إِنَّ اللَّهَ لَيَضْحَكُ إِلَى ثَلاَثَةٍ لِلصَّفِّ فِي الصَّلاَةِ وَلِلرَّجُلِ يُصَلِّي فِي جَوْفِ اللَّيْلِ وَلِلرَّجُلِ يُقَاتِلُ - أُرَاهُ قَالَ - خَلْفَ الْكَتِيبَةِ " .
also referenced under: Book 1, Hadith 205 (In-Book) & Volume 1, Book 1, Hadith 200 (DarusSalam)