Mishkat al-Masabih 4 Prayer كتاب الصلاة 651

وَعَنْ أَبِي هُرَيْرَةَ رَضِيَ اللَّهُ عَنْهُ قَالَ: سَمِعْتُ رَسُولَ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ يَقُولُ: «أَفْضَلُ الصَّلَاةِ بَعْدَ الْمَفْرُوضَةِ صَلَاةٌ فِي جَوف اللَّيْل» . رَوَاهُ أَحْمد

Abu Huraira said he heard God’s Messenger say, “The most excellent prayer after that which is obligatory is one in the depth of the night.” Ahmad transmitted it.