Hadith 2:35
Ibn Mas'ud reported God's messenger as saying, “The Qur'an was sent down in seven modes. Every verse in it has an external and an internal meaning, and every interdiction has a source of reference.” Baghawi transmitted it in Sharh as-sunna .
وَعَنِ ابْنِ مَسْعُودٍ قَالَ: قَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ: «أُنْزِلَ الْقُرْآنُ عَلَى سَبْعَةِ أَحْرُفٍ لِكُلِّ آيَةٍ مِنْهَا ظَهْرٌ وَبَطْنٌ وَلِكُلِّ حَدٍّ مَطْلَعٌ» رَوَاهُ فِي شَرْحِ السُّنَّةِ
Original Reference: Mishkat al-Masabih 238