Sayyiduna Ibn Mas'ud (may Allah be pleased with him) said: "There are two men at whom Allah laughs: One is a man beneath whom is one of the finest horses of his companions; then they meet the enemy and all of them flee, but he stands firm. If he is killed, he dies a martyr, and Allah laughs at him. The other is a man who gets up at night (for prayer) without anyone knowing of him; he performs ablution thoroughly, sends blessings upon Muhammad (peace and blessings be upon him), praises Allah and begins the recitation. Allah laughs at him and says: 'Look at My servant; no one sees him except Me.'"
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 8766