It is narrated from Sayyiduna Ibn Mas'ud (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "The first Book was revealed from a single gate in a single mode (harf), whereas the Qur'an was revealed from seven gates in seven modes (ahruf), containing restraint, command, the lawful, the unlawful, the clear (muhkam), the ambiguous (mutashabih) and parables. So regard its lawful as lawful, regard its unlawful as unlawful, do what you have been commanded, and refrain from what you have been forbidden, take lessons from its parables, act upon its clear verses, believe in its ambiguous verses, and say: 'We believe in it; all of it is from our Lord.'" [Surah Al Imran: 7] This hadith has a sahih (authentic) chain, but the two Shaykhs (Bukhari and Muslim) did not record it.